QuestionQUESTION: 2000 Pontiac Grand Am - 4 cylinder
Problems occur sporadically, not consistently:
1. erratic idle
2. low idle
3. stalls out when stopping at stop lights or stop signs
4. cruise control won't control vehicle speed
5. won't start unless accelerator is pushed
I have had this car in the shop for a week now and they can't seem to figure it out. Things that have been changed: idle air control, fuel filter, air filter, spark plugs %26 boots. Throttle body has been cleaned. Computer has been hooked up, but no codes. Any ideas?
ANSWER: Hi Jessica:
I would look at the hose that goes to the MAp sensor it could be torn split or pinched. Did the problem get worse when any of these parts were replaced? if so and aftermarket parts were put on this. I persobally hate to see any kind of aftermarket fuel control part on a car. They cause more problem then they fix. That aside. A few other things to look at at ground wires on the engine block near the oil filet and any one that are on the transmission to engine mounting bolts. The grounds need to be check by doing what is called a voltage drop test the ground ckts going to the engine control module should not drop more then .020 Volts if any of them do then there is a bad connection or the wire is corroded. Those things are where I would start looking. Good luck :)
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QUESTION: The parts that my husband and I changed were not aftermarket (to my knowledge). Not sure about the idle air control valve. I would assume that the shop I've had the car would check hoses, but I will casually mention it. I was doing research and some of this sounds like a throttle position sensor problem, but no codes are showing. Any chance it could be that and for some reason is not showing the code? I'm a little frustrated as I've had it in the shop several times over the past 1.5 weeks and the problem is still there. Thanks for your help, it's really appreciated.
Answerwith the newer cars (96) and up they have what is called OBD II Trouble codes ther are much more user friendly for the guy/gal working on the car the codes are more precise and will trip sooner then the old OBD systems so if you had an intermittant TP sensor it should have set a code BUT you could have an issue with some sort of interferance with the voltage refrence to the TP sensor and what happens is that change in refrence voltage will induce a throttle % into the engine computer and the computer things the throttle is open and it really is not and it can cause an erratic idle for sure on some of the older GM cars the TP sensor was mated with the gas tank vapor pressure sensor and if that sensor when bad it would take out the other sensors mated to that one and cause some stange issues and NOT set a code. With out the aid of a scan tool to see engien data it's impossible to say what the issue here is but I would take a look at MAP sensor voltage at idle and TP volatge at idle when it's acting up and lastly the tank vapor sensor that sensor should read .05 " h20 to -.05 " h2O with the gas cap off the car if it read a vacuum or pressure the sensor is bad and like I said in some cars with certain engines it would cause ALL KINDS OF WIERD things to happen. Good luck :)
