C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

1987 Stalling while idling, SES Code 34

Old 06-12-2019, 08:47 PM
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Default 1987 Stalling while idling, SES Code 34

Good evening. I have 1987 L98 with a misfire/rough idling that seems to be getting progressively worse over the past few days. I am definitely a beginner but I am capable, I just don't have all the means or experience to diagnose everything myself. I purchased the vehicle about a year ago as a weekend car and a chance to learn. At this point I am thinking the problem is more than I am able to handle alone, and am trying to avoid having to pay to have the car towed to my mechanic. Ill try to provide some backstory about what I have been dealing with as possible, hopefully something will provide some insight. Thanks in advance!

1- Approx. 3 weeks ago I I had the car warming up in the driveway, came outside to find the car had overheated. I found the cooling fan relay to be bad, this was replaced and all was ok. I saw no signs of any further engine damage or blown head gasket over the next few weeks.

2- First thing I began noticing was that the digital oil temp reading would remain at LO for about 10-15 minutes with the car running, even with the coolant temp up to about 200F. Eventually the reading would start creeping up to operating temp, but I don't recall it ever lagging that far behind the coolant temp. Also have recently seen the cooling temp coming out of LO and reading around 100F. Could be wrong as I didn't pay all that much attention previously, but i don't remember the coolant temp ever displaying a reading below 140-150 coming out of "LO". Car still seemed to be running smoothly. This may be completely irrelevant or unrelated but I felt it is note worthy.

3- A few days after is when I first noticed rough idling/misfiring.First thoughts were plugs and wires, but eventually SES threw a code 34 for the MAF sensor. I started off by replacing both MAF relays and cleaning the MAF with proper MAF spray and allowing a day to dry. I put all back together and cleared the SES code, but car was still idling rough. Next step was to pull the MAF sensor wire off and start the vehicle, hoping to throw a code 33 to prove ECM operation. The car begin idling and misfiring substantially worse that before, and was borderline stalling. RPMs on start began at around 800 and leveled off at around 500 RPMs. SES came on but no code 33 was stored when i put the car into diagnostic mode. I ended up reconnecting the MAF and was going to continue researching possible issues. After restarting the car with MAF connected the idle became even worse again. Car was barely starting and would only run a few seconds before stalling. At this point I went from a driveable vehicle to a car that will no longer run just from pulling the MAF sensor to test for a code 33. Not sure what I possible could've affected this badly just by this test that the damage or issue seems irreversible.

4- Since then I have tried disconnecting the battery to clear anything possible faults or "Limp Mode", and have also tried disconnecting the MAF again, but no matter what happens I can not get the car to run to even think about trying to get it to my mechanic.

If anyone has anything at all I could attempt I would greatly appreciate it. At this point to not have to tow my vehicle would be a win for me. Thank you.

Last edited by AC00719; 06-12-2019 at 08:48 PM.
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Old 06-12-2019, 11:14 PM
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When ALDL is grounded to get flash codes, ECM also activates components it controls.The IAC is extended if it's slow to respond idle would be rough and unstable idle, stalling and hard start. If IAC unplug prior to starting engine will idle around 2k. You want to besure throttle body is clear of carbon. A scanner would be handy to monitor MAF. You could check condition of MAF connector.
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Old 06-15-2019, 01:23 AM
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Pull codes again to see if the Code 34 reappears.

If no code I would go back to basics:
-verify proper fuel pressure at start & run conditions
-check for good manifold vacuum

Also check all those vac. hoses in and around the TB for damage.
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Old 06-16-2019, 11:28 PM
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If you have a code 34 for maf sensor, mabey it is out of range. The computer is looking for a certain range.
When you clean it it only takes 5 minites to dry no need to wait. I replaced the connector after cleaning my maf and
I did it for precaution. Maf could be bad I would try to get another to try, A bad maf will cause bad idle/stalling.
The guages for oil and water stay at 0 then start at 100 there is no 0-100.
Good Luck!

Last edited by xrav22; 06-16-2019 at 11:31 PM.
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