Help With Low Idle While in Gear - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 03-16-2010, 02:27 PM   #11
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Originally Posted by Danthurs View Post
Unplug the MAF, the engine may stumble a bit at first and then smooth out. Cleaning the IAT and throttle body is way cheaper and is something that should be done anyways.
I did disconnect the MAF and car ran smoother that with it and idle stayed steady in gear. I am hitting the junk yard in about 2 hours to get one. I'm going to clean the throttle body and IAT while I'm there.

Last edited by azu; 03-16-2010 at 02:32 PM. Reason: Found how to clean IAT
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Old 03-16-2010, 06:34 PM   #12
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To me your fuel trim values don"t make sense based on the following DTC description. I am not an expert in this area maybe someone else might have a better understanding of fuel trim. But your numbers sound a a bit off. The following DTC is from 96 service manual I can't see the specs changing much over 1 model year.

DTC P0171 Fuel Trim System Lean
Circuit Description
To provide the best possible combination of driveability, fuel economy, and emission control, a closed loop air/fuel metering system is used. While in closed loop, the PCM monitors the HO2S 1 signal and adjusts fuel delivery based upon the HO2S signal voltage. A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim values are around 0%; if the HO2S signals are indicating a lean condition the PCM will add fuel, resulting in fuel trim values above 0%. If a rich condition is detected, the fuel trim values will be below 0%, indicating that the PCM is reducing the amount of fuel delivered. If an excessively lean condition is detected, the PCM will set DTC P0171.

The PCM'* maximum authority to control long term fuel trim allows a range between -23% and +16%. The PCM'* maximum authority to control short term fuel trim allows a range between -11% and +20%. The PCM monitors fuel trim under various operating conditions (fuel trim cells) before determining the status of the fuel trim diagnostic. The fuel trim cells used to determine fuel trim are as follows:

Idle, purge commanded (Cell 0).
Deceleration, purge commanded (Cell 1).
Normal driving, purge commanded (Cell 2).
Deceleration, no purge commanded (Cell 6).
Normal driving, no purge commanded (Cell 7).
The vehicle may have to be operated in all of the above conditions before the PCM determines fuel trim status. The amount that fuel trim deviates from 0% in each cell and the amount that each cell is weighted directly affects whether or not the vehicle must be operated in all of the cells described above to complete the diagnostic.
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Old 03-16-2010, 07:40 PM   #13
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Well I went to 4 yards today and could not find one. The cars are all stripped to the bone! I confirmed that the fuel pressure regulator is bad. They just changed the fuel rail with another JY piece. I have a spare new one but the fuel rail they used is not for a 95. It is actually a bit smaller. I believe it is from a 92 or 93 GM. Anyhow I took out MAF and it looked ok and carefully blew some air through it. I'll put it back and replace the FPR and see from there.
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Old 03-17-2010, 06:44 PM   #14
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I changed FPR and now I am really puzzled. Car still runs like crap as if it'* missing at idle, in or out of gear. It misses a bit under acceleration now. Disconnected MAF sensor a few times and car runs about the same, if not worse, and stalls out sometimes. The LT Fuel Trim drops a little but not like it did before I replaced the FPR. New MAF is like $150 but I only want to dump more $$$ on it if that is the problem.
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Old 03-17-2010, 08:07 PM   #15
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Have you checked the the coils and plug wires?
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Old 03-17-2010, 08:34 PM   #16
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Have you checked the the coils and plug wires?
Wires are AC Delco and are a year old. The coils I will check, thanks!
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Old 03-18-2010, 08:56 PM   #17
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I removed all plugs and checked wires. All wires look good (Only a year old) and plugs looked all the same with a white look. Insulators look good with hardly any wear. I checked all vacuum hoses for any leaks, none. Plugs tell me running lean but fuel trim says otherwise. I opened up air box to check for any blockage and filter status and all checked out. I could however detect a gasoline odor coming through cone going to MAF and throttle body. I checked all coils including a spare and here are the results:
Primary Secondary
1) .6 5.36
2) .6 5.89
3) .6 5.30
4) .6 5.69

Primaries are fine but my question about the secondaries. They vary a bit. Is this OK, if so which ones should I use. Would a bad ignition module cause my problem? Is there a way to check it?

My next option if the above are OK is MAF sensor. Odd thing is with MAF sensor on I get a misfire on cylinder 6 and when MAF is disconnected I have no misfire. Also with MAF disconnected exhaust stinks and now there is no difference in engine performance.

I'm confused for the fact that the car seems to be running rich but plugs tell me otherwise.
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Old 03-18-2010, 10:19 PM   #18
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This should confirm MAF question

The Mass Air Flow (MAF) sensor measures the amount of air which passes through the throttle body. The PCM uses this information to determine the operating condition of the engine, to control fuel delivery. A large quantity of air indicates acceleration, while a small quantity indicates deceleration or idle.

The scan tool displays the MAF value in grams per second (gm/*). At idle, MAF should read between 4 gm/* -7 gm/* on a fully warmed up engine. Values should change rather quickly on acceleration, but values should remain fairly stable at any given RPM. A MAF sensor malfuction or MAF signal circuit problem should set DTC P0101, DTC P0102, or DTC P0103.
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Old 03-18-2010, 11:18 PM   #19
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Thanks for the reply. The MAF while scanning shows about 3 at idle and if I raise RPMs to about 1500 it goes to 9. Oddly, no codes. When I disconnect the MAF I get a code though. I am probably going to get a used MAF tomorrow if they still have it. They are hard to find, even new.
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Old 03-19-2010, 04:59 PM   #20
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Did performance worsen after FPR and fuel rail were changed? if so, condition may be due to incorrect parts. May be causing fuel pressure too high which will cause a rich condition. Is the fuel smell coming from EVAP can?
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