hesitation/hunting idle
08-18-2002, 03:16 AM
#1
1st Gear
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Join Date: Aug 2002
Location: Glencoe, IL, USA
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hesitation/hunting idle
I'll give you the whole frustrating story, maybe it will help diagnosis. Bought my 93 C2 about a year and half ago from dealer, came with aftermarket exhaust and chip. Surprise, didn't pass emissions. After really leaning on them, they replaced exhaust with used stock unit and put stock chip back in, which I tracked down from prior owner. With that, passed emissions but started having problems with intermittent hesitation and hunting idle. Dealer couldn't find a problem, no error codes, said Porsche is a high performance car, idle not perfect. Wrong answer. Problem got to point where electrics cut out as idle swung low, then started stalling from time to time. Car only has 30K miles, was due for sevice, so local independent mechanic trained in Porsches and I decided to pull engine, do service and hit everything that's tough to get to when engine in place. With respect to things that may affect this problem, adjusted valves, replaced plugs, head temp sensor, O2 sensor, battery (which tested weak), DME relay, idle speed motor, probably something else I have forgotten. Checked distributors, all looked happy. After we were done, everything was great. Then slowly, hesitation when accelerating when cold developed and has gotten worse. Then my old friend hesitation/hunting idle reappeared. Only does it sometimes, and so far I have been able to address it by turning the car off and starting it again, whereupon it goes away. However, when I do this, electrics seem to freak a bit as presets on radio either get scrambled to new stations, or get cleared, like it was disconnected. Help!
08-18-2002, 04:28 AM
#2
Brian:
Your problem may be the battery, charging system, or faulty grounds. If the radio is resetting itself, it means that it's seeing power being removed from it. Addtionally, as voltage levels supplied to the ECU drop, the ECU will itself begin to malfunction. The ECU NEEDS a minimum voltage level set to operate properly. Once it drops below those levels it's behaviour will likely become erratic, and if disconnected long enough, it will reset itself and go into "learning" mode.
When a battery drains, it develops a higher internal resistance, and thus cannot produce as high a voltage to the car. Once the battery is unloaded (by turning the car off) the internal resistance will decrease exponentially, and it will suddenly act like a newer battery. Since you can get the car to run OK for a while by turning it off and then restarting it, it sort of implies to me that your car isn't being fully charged. Once the car is running, the electricity is supposed to be powered by the alternator, not the battery. This to me implies that your alternator isn't putting out enough power, or there is something preventing it from delivering power (bad grounds or bad supply wires).
There's a lot that can go wrong with the cars, but that's my shot at your problem. Hope it helps.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
Your problem may be the battery, charging system, or faulty grounds. If the radio is resetting itself, it means that it's seeing power being removed from it. Addtionally, as voltage levels supplied to the ECU drop, the ECU will itself begin to malfunction. The ECU NEEDS a minimum voltage level set to operate properly. Once it drops below those levels it's behaviour will likely become erratic, and if disconnected long enough, it will reset itself and go into "learning" mode.
When a battery drains, it develops a higher internal resistance, and thus cannot produce as high a voltage to the car. Once the battery is unloaded (by turning the car off) the internal resistance will decrease exponentially, and it will suddenly act like a newer battery. Since you can get the car to run OK for a while by turning it off and then restarting it, it sort of implies to me that your car isn't being fully charged. Once the car is running, the electricity is supposed to be powered by the alternator, not the battery. This to me implies that your alternator isn't putting out enough power, or there is something preventing it from delivering power (bad grounds or bad supply wires).
There's a lot that can go wrong with the cars, but that's my shot at your problem. Hope it helps.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
