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Full Lean Idle after clutch install

2K views 24 replies 7 participants last post by  3KGT-VR4-93 
#1 · (Edited)
Car had no idle issue before I did the following:
Clutch
Flywheel
EGR Block-offs (also put 10 ohm 1/2 watt resistor at connector & plugged both vacuum lines)
Downpipe/Rear pre-cat elim
Oil Change
Fuel Filter
Rear main seal


NOTE: I checked my ECU caps, ECU looks perfect inside

Car starts fine and idles over 1k rpm and A/F is 14.5-15 then after about a minute or two, it idles lower /sounds quiet and rough, A/F is full lean "--" on the AEM WB. The A/F does change to ~15-17 while driving.

Any idea on what could've gotten messed up during my install? Everything "looks" fine, no CEL. I didn't touch the throttle body adjustments, the ECU should re-learn the curve quickly even after having the battery disconnected for a few weeks, right?
 
#2 ·
Same problem on my 95 NA ATX. Lean at idle full lean or 15.5 to 17-18 or off the gauge some day. While driving its normal but I notice it sweeps from like 14 to 15.9 so something is off very off. It use to only sweep from 14.6-15 and would idle from 14.7-15.

Cant figure out what the issue is. I have checked everything I can think of.

Or have I
 
#3 ·
Did it happen after you did any work on your car? Could be IAC/ISC, O2 sensors, coolant temp sensor, throttle body/TPS adjustment, leaking ECU Caps, etc... Your issue could be O2 sensors from the way it sounds.
 
#8 · (Edited)
I'll definitely check for leaks, I looked around and didn't find anything disconnected.

Checked O2 sensor Voltage
From the blue wire while it was connected. I was getting ~90mv on the front O2 and ~105mv on the rear at idle.
The O2 should fluctuate between .1-.9V and I'm getting a pretty steady .09 to .1V

Disconnected MAF
Car went from full lean to ~11-12 A/F with MAF disconnected, which is expected.

My symptoms seem to point to a sensor, initially when I start the car it shows 14.7 A/F, then after about 45-60 seconds, it gradually creeps up to fully lean. I also noticed before that even when driving it will stay on full lean, once in a while it will go to 15-17 a/f while cruising, seems like the O2's are the culprit, I'll report back
 
#11 ·
That's a great point, I actually fixed an exhaust leak I had where my test pipe meets the exhaust.

EGR related? My block plates don't leak. I took my resistor out and put it back in, same result.

I never had the wideband on the car before my clutch/dp install. It could have always had a lean idle so I might have to check everything related to the idle instead of thinking that it was something I may have hit during the install.
 
#12 ·
is the wideband brand new or used? and what angle and in relation to a clock how do you have it installed and where at in the exhaust? you may want to do a compression/leak down test. burnt exhaust valves can do this also
 
#14 ·
any exhaust leaks around the WB sensor? do you have any data logging software? i would like to know what your primary 02 sensors are reading. if not get a volt meter and tap into the signal wire of the primary 02 sensor with the car running and see how many volts its showing. it should cycle between like .4-.8v somewhere around there.
 
#16 ·
so your def running lean. sounds like you have a weak fuel pump/ clogged line/ dead injector(s)/ or a bad fuel pressure regulator. i would look into your fuel pressure and see what you have and start from there.
 
#19 · (Edited)
#22 ·
Does you A/F go richer when you tap the gas at idle and while cruising? Did you take off your intake and look at the MAF? My car only had exhaust and a K&N when I bought it and the previous owner gutted the MAF.

I'd raplace the O2's even if that's not the problem, you never know. I got these, they fit exactly like stock, no splicing,etc...
DENSO 234-4631 Oxygen Sensor
DENSO 234-4633 Oxygen Sensor
 
#23 ·
I had already replaced O2's thinking it could be part of the issue and I used Bosch sensors that I wired in (cheaper and im a wiring guru :) ) I however found my issue yesterday, my CAS was bad and the mfi relay was as well, issue is resolved now, altho now that i've said it works, something else will go shortly. :shitsweak:
 
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