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Old 03-20-2017, 12:11 PM   #1 (permalink)
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Default Hard starting when warm...only sometimes

Now I search through the forum and this seems to be a common problem, but could not find a definitive answer except from 2009, SkortchGT stated a solution was non-resistor plugs, recommending NGK BCP6ES's (stock heat range).
This has been happening for years, on rare occasions, as the weather gets warming, to my 1992 VR4 (now 160k) I have owned since 1995 (w/57k). Annoying+ embarrassing as some have said. Now I have a 1996 VR4 Spider, weather here got to 80, drove the car 5 miles, turn it off for a hour, and BINGO would not start! WHAT! So now I look for an answer here.

Cars turn over, seem like they are starting to catch but dont. keep trying, maybe hold the throttle wide open and it will chug and chug sputter shutter shutter kind of barely running then die. Eventually you will get it to kind of catch, step on the gas and with a POP out the exhaust it is running! Now the old car you have to rev it up a bit to get it smooth, but the '96 just started running smooth. It acts like "Vapor Lock" as others have described it, either lean or rich in fuel.
I saw one suggestion of the fuel pressure regulator sticking, now that makes sense or the solenoid they use to give it vacuum, I think it is the same as the boost control but I could easily be wrong. It there a better replacement fuel pressure reg I could try?

Chime in anyone, there must have been an answer by now
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Old 03-20-2017, 01:09 PM   #2 (permalink)
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Default Re: Hard starting when warm...only sometimes

I've been into these cars for a long time, and heard all the rumored fixes, and I'm here to tell you that I haven't seen anything fix it. I've messed with these cars with some of the really knowledgeable people too.

My personal belief is that there is an issue in the base code of the ECU. But I have no evidence to back it up, other than my experience.
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Old 03-20-2017, 01:23 PM   #3 (permalink)
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Default Re: Hard starting when warm...only sometimes

The most probable answer to me was that because the fuel has changed to part ethanol the ethanol boils (much lower boiling point than gasoline) and gives you air in the fuel rails so it's hard to start. I have seen people wrap their fuel rails in insulation but from what I recall nothing worked to well... but this is just what I read on here. I wonder if you could try some fuel with out ethanol to see if it makes a difference
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Old 03-20-2017, 02:06 PM   #4 (permalink)
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Default Re: Hard starting when warm...only sometimes

Its called heat soak. Its super common. I have it, but not to that extent. What helped me a lot was changing out the Idle Air Control valve that's next to the throttle body.
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Old 03-20-2017, 05:32 PM   #5 (permalink)
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Default Re: Hard starting when warm...only sometimes

An intermittent bad coolant temperature sensor can make it impossible to start the car at times. I solved this problem with two cars, it was easy to determine the problem when you can see negative coolant numbers on the LCDBC screen. Unfortunately the ECU does not trigger a CEL code because the coolant sensor is not 100% broken.
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Old 03-20-2017, 05:59 PM   #6 (permalink)
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Default Re: Hard starting when warm...only sometimes

Nice job to plug your own product!!! haha... but it is an awesome product/

There quite a few things that can compound the problem. I had a bad IAC that was not stepping properly, which was easily seen via the LCDB, that wasn't triggering a CEL. Replaced that and it stopped some of the warm start up issue.

These cars were designed in the late 80s so the ethanol/fuel mix is very plausible. especially since giving it gas for a few seconds makes it go away. Do cars running e85 have the issue as well?
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Old 03-20-2017, 06:36 PM   #7 (permalink)
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Default Re: Hard starting when warm...only sometimes

my car's poor hot starting/idling was fixed when april rebuilt my throttle body. I don't know if it was IAC or throttle shaft seals, but it's great now.
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Old 03-20-2017, 11:45 PM   #8 (permalink)
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Default Re: Hard starting when warm...only sometimes

I don't think I ever experienced this problem before. Then again my IAC is brand new aftermarket.

Then a year later I had April rebuild the throttle body. Maybe start with the IAC? I believe the aftermarket part is 3000gt IAC AC99.
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Old 03-21-2017, 12:14 AM   #9 (permalink)
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Default Re: Hard starting when warm...only sometimes

I'll start with the coolant temp, look for readings that make sense, then check your fuel pressure, if you activate the fuel pump via the black test port it should build the 40psi or so instantly, if doesn't stays that way for at least a few minutes, check your sending unit, there is a little O-ring that if gets bad it will give you hard starts and also poor performance, also FPR for leaks, injectors, check all your vacuum hoses and the IAC, I had a similar problem, not as bad as yours but it ended up being the starter, it sounded fine, turned the engine quickly but somehow caused a bad start, now it barely turns and the engine fires up.
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Old 03-21-2017, 12:26 AM   #10 (permalink)
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Default Re: Hard starting when warm...only sometimes

Coolant temp sensor. The ecu needs to know how much fuel to inject as per temp. If its getting an improper reading it wont know how much fuel to add. Sensors are cheap and easy to fix just replace
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