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So today we all get in the car to go somewhere, & 2 blocks from the house the rpm gage starts going nuts way up to 3500, down to 1k up to 2500, 5000, down to 2k, it's crazy! Was going up a very slight hill (if that matters), but the actual engine rpms are not matching what the tach gage is saying at all. I step on the gas a bit but can't settle the tach at all. Engine sounds very rough it's struggling as if I put the wrong type of gas in it (never sounds like this!).

The check engine light blinks off & on, then stays on, and goes off as I get to a stop sign, and then it takes off fine! I go around another few blocks, all in 1st/2nd gear, no problems. Engine sounds a little loud but not sure if that's just because the radio is off for once.

Then take it on the freeway about 3 miles, 4500rpm on the tach & engine rpm like it should be, take the offramp down to 25mph, turn around back on freeway at 50mph engine sounds fine again, then the rpm gage starts going crazy again all over between 1k & 6k but the engine rpm is staying about 3500rpm, then finally seems to lose engine rpms, I step on the gas, doesn't want to respond. Check engine light stays on. Make it off the freeway & limp home in 1st gear at 20-23mph at 2100rpms, rpm gage stays true to engine rpm, check engine light won't go off. I blow a few stop signs and park it.

Waited an hour to think about it, then start it up to try & get it up the driveway steep hill, no problem, no wild tach, no check engine light. Sit in the driveway at idle & the rpm gage that usually sits about 900-1100 along with the engine rpm stays true. Well...

I get on the forums & start searching. I disconnected the ECS in the dark, started up the car again, no check engine light, but just let it idle --- the tach slowly bounced up from 900rpm to 1500, 2200, 2600, then I shut it off. Foolish to think disconnecting the ECS would do the trick, but desperate enough to try.

The problems on the forum (and the vids on youtube) with the wild tach all seem to say that the engine rpm is wild too, but my engine rpm at idle stays typical, and doesn't fluctuate on the freeway speeds with the tach at all, it's just the gage that's bouncing all over the place. I didn't dare step on the gas in the driveway to see what it does (respond or not). Should I?

*I did adjust the idle rpm up a bit about 5-6months ago because it was wanting to die w/800rpm for idle, it couldn't just stay at 800, it would bounce between 700-1100 like it was trying so hard to be 800 but coudln't. I set it at 1200rpm and the car hasn't complained, until this (related or not, i don't know). The ECS has been broken for at least 2yrs stuck in sport (that's all I use anyways so fine).

It's a stock sl... runs good (not great) it's been hesitating a bit when I step on it, for a while now, but it's old so? not sure if that's related. The lifters tick but expected at 250k miles. No weird smoke out of the pipes, and no weird smells in the car. Oil's typical.

AND it is not dying. Even with the CEL on, limping home, it didn't die once or even come close to it. Will sit there in driveway idling, no problem, just don't dare drive it as is.

Please help me with searching/finding what this is. I've been looking for hours, no symptoms are matching up to forum/youtube videos so far. Maybe I'm not searching with the right words?

Sorry so much typing, just trying to explain ...

Much much thanks :)
 

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*I did adjust the idle rpm up a bit about 5-6months ago because it was wanting to die w/800rpm for idle, it couldn't just stay at 800, it would bounce between 700-1100 like it was trying so hard to be 800 but coudln't.
Classic signs of IAC needing cleaning.

Your tach is PROBABLY just bad. BUT... my experience is aftermarket alarms do wacky stuff to the instruments, so check for a black box under the dash that doesnt say Misubishi on it.

-SP
 

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Discussion Starter #3
Oh thanks! I did just pull fuse 19 to reset the ecu, started it up, idle rpm still not settled on tach, and the cel is on at idle now in the driveway at cold start, so happy to clean the IAC. Wonder if I can get it off in the dark? LOL.

Thanks :)
 

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Discussion Starter #4
Classic signs of IAC needing cleaning.

Your tach is PROBABLY just bad. BUT... my experience is aftermarket alarms do wacky stuff to the instruments, so check for a black box under the dash that doesnt say Misubishi on it.

-SP
WOW. I knew that IAC looked familiar. That's the very first part I replaced on the car, 2yrs exactly after I bought it. so very close to 100k miles ago :( Back then it was replaced because the idle was stuck too high no matter what. Gah, it's like it's happening all over again a decade later! :(
 

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Discussion Starter #5 (Edited)
Trying to figure out what to try next. Is there a way to know if the Tach is just bad? Search says tachometer is electronically fed from the PTU - if that IS the problem would that make the cel be on?


Going through the sensors it could be by the process of elimination:

Car runs at idle so Probably not the crankshaft position sensor:
Hint 5: If the engine can be run at idle even though the crankshaft position sensor reading is out of specification, troubles are often in other than the crankshaft position sensor.

car Will idle and engine rpms are not reflected on the rpm gage so Probably Not the MAF mass air flow sensor:
Symptoms don't match -won't idle, dies, and engine rpms are pretty much reflected on the rpm gage

IAC: Dirty, yes, but not stalling at idle so probably not it
Idle Air Control Valve failure symptoms
Symptoms don't match-A faulty IAC will cause stalling problems at idle.

Getting spark no problem so Probably not the Power Transistor Unit (PTU):
Symptoms don't match-The Power Transistor Unit is a common point of failure for the ignition system. If you are not receiving spark and have eliminated other parts from being bad, look into Stealth316′s PTU guide to find out how to test and diagnose a bad PTU.

Eh, think I found it... http://www.3si.org/forum/f35/what-would-cause-tach-do-video-543361/#post6490159 So now I think it probably iS the pTU! Going to go after that 1st today!
 

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Discussion Starter #6
On the chance it MAY be the ECU, I just took it out & took some pics to be sure nothing looked bad on the board / capacitors. It looks OK to me, what do you think?











 

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Discussion Starter #7
One more angle on the ECU. I think it looks like maybe this capacitor had leaked in the past, but had been replaced maybe because it looks fine now? No swelling or leaking around the capacitor... But looking at the board it's got some gold looking stuff on it where it should just be green? Not sure :( Sharing just for others to see to compare if they need to.

 

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Discussion Starter #8
ECU question Re: Tachometer freaking out, engine rpms not, cel on

Classic signs of IAC needing cleaning.

Your tach is PROBABLY just bad. BUT... my experience is aftermarket alarms do wacky stuff to the instruments, so check for a black box under the dash that doesnt say Misubishi on it.

-SP
Hey I saw on a previous post you sent your ECU to Rymer ( http://www.3si.org/forum/f36/why-does-my-ecu-keep-dying-540616/#post6458828 ) How did that work out for you?

I'm getting more than worried about there being a past or present problem with the ECU at capacitor C105 and a possible multiplex issue but not sure
because I have NO IDEA what a multiplex is!

I read all over to replace the capacitors, but sometimes that doesn't do the trick, but do it anyway. Did sending it to Rymer help you?
 

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This is NOWHERE near as hard as you are making it. I guess you just want to do extra work.

IAC usually needs cleaning, ALONG WITH the throttle body. You have to test it with a multimeter to make sure none of the coils are shorted or open.

Car runs right? ECU is good
Car runs right? PTU is good.

I have never has rymer do any work for me. His posts have indicated he does have the knowledge and talent to repair ECU's that nobody else has.

My first post gave you all the info you needed.

-SP
 

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did you go to a parts house and have them pull the codes? that to me would be the first logical step.

if your tach and engine miss firing (but not in unicien) I would look at what triggers' the tach... sounds like a sensor bad... but I really do not know what can be the cause of this. IAC valve, I would not guess that to be the cause, but then again,... I am not that famular with the sensors and controls on this engine
 

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This is NOWHERE near as hard as you are making it. I guess you just want to do extra work.

IAC usually needs cleaning, ALONG WITH the throttle body. You have to test it with a multimeter to make sure none of the coils are shorted or open.

Car runs right? ECU is good
Car runs right? PTU is good.

I have never has rymer do any work for me. His posts have indicated he does have the knowledge and talent to repair ECU's that nobody else has.

My first post gave you all the info you needed.

-SP
Just because the car runs does not mean the Ecu or crank sensor is good, the Ecu will look at the cam sensor and estimate where the crank is based on inputs from the cam sensor if the crank sensor is bad.

Try swapping your Ecu out with a known good one. I bet all your issues go away.

I had the same issues you are having and they just got worse over time until the car did not run. It was throwing a crank sensor code but I had already changed both sensors. I swapped my Ecu and everything was fixed. I'll show you pictures of mine.
 

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Discussion Starter #13
This is NOWHERE near as hard as you are making it. I guess you just want to do extra work.

IAC usually needs cleaning, ALONG WITH the throttle body. You have to test it with a multimeter to make sure none of the coils are shorted or open.

Car runs right? ECU is good
Car runs right? PTU is good.

I have never has rymer do any work for me. His posts have indicated he does have the knowledge and talent to repair ECU's that nobody else has.

My first post gave you all the info you needed.

-SP
YES you're right! I am making this harder than it has to be :( I do that a lot. Couldn't even sleep last night worrying about what's actually wrong. So I'll follow your advice & pull the throttle body and try to clean that out, never did that before but the IAC is no problem to clean. I'll have a look at the ECU bottom side and see if I think I can replace the capacitors myself or not (should be able to, not sure yet).

did you go to a parts house and have them pull the codes? that to me would be the first logical step.

if your tach and engine miss firing (but not in unicien) I would look at what triggers' the tach... sounds like a sensor bad... but I really do not know what can be the cause of this. IAC valve, I would not guess that to be the cause, but then again,... I am not that famular with the sensors and controls on this engine
From the forum searches it looks like the PTU triggers the tach, so I ordered that part this morning. Watching videos of other people's tach doing the same thing as mine & they said it was the PTU, so worth a shot. Though the IAC is probably going bad hopefully cleaning that will make a big difference like Speedy says.

I did just find this morning the local parts house will do the OBD codes for me, I'm just scared to death to drive the car over there with it acting the way it is. Looked up the paperclip method for the OBD I and thinking about trying that.

Just because the car runs does not mean the Ecu or crank sensor is good, the Ecu will look at the cam sensor and estimate where the crank is based on inputs from the cam sensor if the crank sensor is bad.

Try swapping your Ecu out with a known good one. I bet all your issues go away.

I had the same issues you are having and they just got worse over time until the car did not run. It was throwing a crank sensor code but I had already changed both sensors. I swapped my Ecu and everything was fixed. I'll show you pictures of mine.
I REALLY appreciate the ECU pics, I'm going to have to pull mine out again and have a look at the bottom. I think I can re-do the capacitors but I'm not sure how bad it is yet, so we'll see... I would LOVE to switch out the ECU with someone local but I'm in the Portland, OR metro area & don't know anyone local that has one to test with. The few 3kgts that I do see are not 91-93 anyways. I keep looking at the crank sensor possibility but decided on trying the PTU first, since that's what feeds the tach apparently.

I *think* this is where I'm at now:
  1. clean the IAC and throttle body, figure out how to use the digital multimeter I have to test out the coils
  2. pull out the ECU again and look at the bottom, replace the 4 capacitors on the ECU if I can, if not send to Rymer if needed
  3. replace the PTU
  4. test the car again
is that still making it too hard?

Thank you all so much for the help & advice!
 

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Discussion Starter #14
Got off the throttle body but still waiting on the wd40 to work on the screws to take this apart more.





Couldn't figure out how to unplug the plugs in the dark & got sore with the flashlight in my mouth while struggling in the dumb rain, so the other parts that attach are still stuck under the hood. Will tackle those in the daylight tomorrow.

Will work on cleaning this up tonight though so at least getting something done while waiting for the PTU.
 

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Discussion Starter #15
Just a note for anyone else cleaning the same thing, that o-ring visible in the 1st pic stretches like crazy when it's taken out even carefully, so have a spare ready or be ready to get another one. It was in good shape when I took it out to clean around it, but there's no way in the world it's fitting back in there.
 

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did you read the check engine light? could be a misfire - like a fouled spark plug. mine did the same thing when i fouled a plug, with the check engine light and all, but never came close to dying.
 

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Just because the car runs does not mean the Ecu or crank sensor is good.
That may be true in a few rare instances. OP said his car ran OK but his tach was wacky. Usually when either of those parts are the problem there is misfires and hesitations which he did not mention.

93driver-

You dont have to REMOVE the TB to clean it. But then agaion you like to make more work for yourself.

Most, if not all, parts places will only read OBDII codes. Thats 96 and up.

I still havent seen you report that you looked for an aftermarket alarm yet.

-SP
 

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Discussion Starter #18
That may be true in a few rare instances. OP said his car ran OK but his tach was wacky. Usually when either of those parts are the problem there is misfires and hesitations which he did not mention.

93driver-

You dont have to REMOVE the TB to clean it. But then agaion you like to make more work for yourself.

Most, if not all, parts places will only read OBDII codes. Thats 96 and up.

I still havent seen you report that you looked for an aftermarket alarm yet.

-SP
I still haven't seen an aftermarket alarm anywhere on the car... but there was a half-removed radar detector. The wiring is there, but no unit. They tucked the wiring up under the headliner so I have no idea where it comes out at the other end to be connected into the system?! I guess I need to figure out how to remove the headliner, too :(

ha-ha at me, I did remove the TB already, dang it. I cleaned it for hours tonight with q-tips and paper towels. At least it's clean now *sighs*.

The auto parts place where I was looking for parts nearby says they do OBD 1 and 2 code reading and clearing for free.

There's no misfires so far as I heard or felt (rest my hand on the steering wheel and felt good pulse of the engine heartbeat), it just sounded loud/ rough as hell, like loud not misfire, like it wasn't getting enough gas or maybe too much?

Sounded like it was struggling (engine much louder than normal) when the tach first went crazy, but no jerking or coming close to dying, then sounded normal in town to the freeway and on the freeway for about 3-4miles, and then the tach went nuts again on the freeway and it was struggling sounding again, yet after shifted down to 2nd & 1st it was normal sounding all the way limping home. I didn't feel or hear a miss through all that, and it never tried to die.

Once I got it home and idling in the driveway it sounded perfectly normal! But the tach was jumping all over the place again with no change in the idle rpm.

It's had very very slight hesitations for months, but I figured that was the cold weather, it always hated cold weather. Nobody else would notice the hesitations they were so slight, barely noticeable unless you're used to that *instant* response these cars have.

There was no engine rpm response when I stepped on the gas on the freeway when the tach started going nuts. I don't know if that's hesitation or just freakin ignoring the extra gas like it already had too much so extra didn't matter?

Sorry I don't know how to be more clear than that, painfully aware I'm being such a girl about this. I do very much appreciate your input on this!!! Thank you.

futurevr4man said:
I'll check the plugs this week while I'm in there anyways looking over everything else, might as well & never know it could be more than just 1 thing!
 

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Discussion Starter #19
Pulled the ISC/IAC off today and this is how bad it looks:





I do still have the old one, from 2002... wondering which part of it goes bad, the top knobby part or the bottom plug-in part; thinking about taking half of the old one and half of the new one & putting them together instead of buying a new one. #1 because I hate waiting for parts & #2 because it might just work!

btw for anyone else, here's the link Stealth 316 - ISC Servo Motro
 

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Discussion Starter #20
Sloppy IAC wow yep

Eh, looks like I'm ordering a new IAC.

Story: pulled the IAC and yet I could NOT find exactly HOW to ohm test, but I did find this main page
Which says: "If you can rotate the plunger easily with your fingers at all axially around the major axis, it is getting loose and sloppy. "

So I grabbed it to see if I could turn it, and YES it turns super easily, not all the way around but a good degree around amount. Then I grabbed the old bad one from the last time I replaced it (2002), and the plunger in that old one didn't move as much as this one that I just pulled. Sheeesh, my poor baby was making up for this bad IAC all this time:( I have much guilt. Grrr.

Excellent call Speedy! I'm your newest post stalker for good info ;)

I don't know how many miles I put on this, but I'm guessing really close to 90k... TOO MUCH.
 
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