1993 Pontiac Grand Am 3.3 litre high idle.

Tiny
DIRTY HARRY
  • MEMBER
  • 1993 PONTIAC GRAND AM
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 115,000 MILES
Hello all. I have a 93 Grand AM with a 3.3 litre with a high idle. (2000-3000 RPM's hot or cold). I replaced the IAC with a known good one, cleaned the throttle body, the MAF, and the IAC passages in the throttle body and still have the same high idle. Checked for vacuum leaks with carb cleaner with none found. I have an OTC scan tool and have scanned some data and what seems weird is that the IAC counts stay at 110-120 whether in park or in gear at 1300 RPM's. I've heard the IAC counts should be down around 20-30 or so. The TPS scans ok between.27 and 4.0 from idle to wide open throttle. O2 sensor is switching back and forth OK too. I just got this car and have no troubleshooting or wiring diagrams. I'm thinking maybe some wiring issues between the IAC and PCM? I'm at a loss on this one! Any ideas?

DH
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Saturday, October 25th, 2008 AT 9:22 PM

3 Replies

Tiny
MMPRINCE4000
  • EXPERT
You most likely have a vacuum leak somewhere, vacuum line, brake booster, intake manifold gasket, fuel injector O-ring.

If you put the car in diagnostic mode (jump terminals A and B of the ALDL), this should move the IAC to the fully closed position (you should hear it buzzing).

If not then the IAC may be bad.

But the IAC is designed to control the idle within a range of about 700 rpm, so I still think you have a vacuum leak somewhere.
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Sunday, October 26th, 2008 AT 8:18 AM
Tiny
DIRTY HARRY
  • MEMBER
You most likely have a vacuum leak somewhere, vacuum line, brake booster, intake manifold gasket, fuel injector O-ring.

Thanks for the reply. I jumped the data connector and the new and old IACs both work. Then I replaced the PCV valve for $2.50 for the heck of it. I also started to disconnect fuel injectors to see what would happen and I could disconnect all three on either side of the engine with hardly any rpm difference, then when I disconnected a 4th cylinder it would get rough. I'm wondering if the fuel pressure regulator is inop. Causing it to dump fuel all the time and possibly not returning much to the tank. Who knows, I'm going to dig out my vacuum simulator/gage and look up the troubleshooting for the fuel regulators. I have to look for my fuel pressure guage as well. Might just go to the junkyard and see about a used regulator to try out.

Dave
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Sunday, October 26th, 2008 AT 6:45 PM
Tiny
MMPRINCE4000
  • EXPERT
The FPR should be on the ruel rail, disconnect the vacuum line and look for gas in the line, if present then the FPR diaphram is ruptured and the FPR must be replaced.
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Tuesday, October 28th, 2008 AT 10:21 AM

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