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Hello Mr.Aguirre, you may have a dirty throttle body, or a sticking or defective idle air control valve. You can clean the throttle body and throttle plate with a cleaner made for this, use and old tooth brush to clean both side sides the plate, then wipe out with a rag. You can remove the IAC valve and give it a cleaning also. If you still have the problem,replace the IAC valve. Here are some illustrations .I hope this helps ,Jerry.
Hello Mr Aguire,sorry to hear that the IAC and cleaning didn't fix your problem. I did some searching for similar problems on your model car and found many reasons for the idle problem. You didn't say if it happens only cold or at all times. If cold I found that things like a vacuum leak,to high oil pressure causing pumped up lifters have been found. I will send one of the help requests and what was found.It turned out to be a rare problem that took some time to find. To check your problem out further would require some in depth testing with a scan tool, to check the sensors and fuel trims when this problem occurs. Sorry what I suggested didn't help,it does cure the problem 90% of the time, sending this to try to help you get some direction to the car fixed,no need to hit accept again, Jerry.
1996 Pontiac Sunfire Engine: 2.4 L / 146 CID / 4 cyl / Gas / DOHCFuel: Fuel InjectionIgnition: DistributorlessTrans: 4-speed Automatic Transaxle (Electronic)Mileage: 141,000 miEmissions: OBD-II CompliantVIN: 1G2JD12T6TMisc Data: NO CodesSymptoms: Poor Idle Quality, Hesitation, Surge, Cuts out, Stall, Misfire, Poor Fuel EconomyOccurs: Cold, Hot, Idle, After a Hot Soak, IntermittentlyMore Info: Test results & repair history included below_____________________ ORIGINAL MESSAGE _____________________Argh! This vehicle has been driving me nuts for the lastcouple of days. The problem is it only acts up veryintermitantly with NO CODES... What happens is after theengine warms up to operating temperature it will begin tostall/cut out down to 300rpm then recover to 900rpm then stalldown to 300rpm and repeat indefinatly. It will do it after acontinuous run from cold to warm, or from a warm restart after30min-1hour after a shutdown. Cannot perdict when it will doit. You can rev the engine up to 2000rpm and you can stillfeel a slight mis and the engine will buck periodically. With the engine acting normally I drove it on the highway anddoing 100Kph(55mph) and mashine the accelerator there is nopickup, just a lot of noise, you have to manually shift thetrany (auto) and you hear what sounds like an exhaust leakwhen the engine is reved above 4500rpm under load only. Thereis some acceleration but nothing to write home about. There isbetter part throttle acceleration at these speeds than at WOT.I disconnected the iac with the engine idling normally at900rpm and drove it throught he city with multiple stops andstarts with a 45minute shutdown and restart with no problem.The engine did stall after it sat and cooled down and tried tofast idle(3 hour cooling with outside temp at 6^C (44^F).There is oil leaking from the cam cover and from around theoil presure sensor boss. At the time I hooked the scan tool up to it, it behavedperfectly for over an hour of trying to get it to misbehave.Even when the idle is surgine the alternator is putting out13.8V+ at 300rpm, Here is what I have for the only real scansession: Idling At 900rpm.ECT 115^F(Verified w/ Thermometer)TP Sensor .35V (Operated within Spec)Baro Pressure 11 in-HgLT Fuel Trim -17.2%ST Fuel Trim 0 - -7% (cycled from 0 to -7%then Reset to zeroand repeated)Map Voltage 1.37V (operated within spec)B1S1 O2 Operated Between 300-600mVB1S2 O2 Operated Between 400-500mVI have looked at tons of iatn posts from Oil pressure totiming belt skipping to reflashing the comp. I'm not reallyinto throwing parts at vehicle untill i'm entirely desperate,I'm not there...yet! I know iatn's experiance will let me makethe correct choices and repairs. Thanks in advance, I'll update when I obtain some morerelavent information.Matthew___________________ TEST AND REPAIR DATA ___________________Checked for codes and none were found.RELATED REPAIR HISTORYReplaced IAC with known good unit with no change indrivability. Replaced Ignition Boots, Plugs Were ReplacedThree Years and 40K ago.______________ COMMENTS ADDED ON Dec 29, 2007 ______________Thanks For Your Patience. This vehicle came in for unrelatedmintenance and we did the back pressure test. It was perfect.At idle the gauge was below 0.25psi, at 2000rpm the gauge wasaround 0.25psi, and at 4000rpm the gauge was between 0.25psi &0.50psi. This was done at operating temperature, before andafter the cat, and with the engine running perfectly...for an11year old quad4! The noise that is being heard is from the balance shaft chain.The chain tensioner was broken causing it to vibrate and makethis noise. Thanks again for all who replied Matthew____________________________ FIX ___________________________Thanks to all who replied, I'm with the majority and believethat there is also an exhaust restriction, but after thevehicle was repaired the customer chose to take the vehicleand has not returned yet for the back pressure test. The problem turned out to be a faulty diode within thealternator. WHen I looked throught he other IATN posts, othershave had leaking AC current drivability problems. I hooked myDVOM between the positive battery terminal and alternator caseand recorded these reaedings before replacing. At idle beforethe car would surge and idle rough there was 0.050V of ACcurrent. when the idle began getting rough and cylinders wouldstart to drop out the AC volts went up to 0.100V, when thevehicle started to surge the AC Volts whent up to 0.200V, andwhen the vehicle would stall the AC volts would rise up to0.355-0.400AC-V before the engine stalled out. The quality ofthe idle was in direct proportion to the amount of AV Currentbeing produced. If I get the vehicle back to do a backpressure test I'll update this post with the readings. Thanks Again.