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Random super high idle


Cparkes foo
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Hi my car is a 94 3100 gp most of the time it runs great as it has just under 50k but recently it has started reving to 2500 to 3000 rpm, i have replaced iac,tps,map,ats,ecu,plugs wires throttle body gasket,and rubber grommets for pcv, problem has not changed. It has got a 50/50 chance if it runs right or not any suggestions no engine codes plz help

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Try disconnecting the IAC harness AFTER you shut down the engine (shutting off the engine bottoms out the IAC pintle).

 

Leave the harness off the IAC & try to restart the engine, it should not fire seeing as the IAC is closed, if the engine does fire your sucking air in from somewhere else or the IAC is not closed.

 

Pull off your intake snorkel and peek into the throttle body, the blade should be completely closed, if it not then adjust the throttle stop screw so it is just closed all the way but does not bind.

 

Let us know what happens after you're tried these measures.

 

 

Not setting a code is odd, if the idle is out of range (300 rpm) for more than 50 secs the PCM will set a code.

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Unplugged iac wont run and throttle body is closed still have to check grounds at a glance they all look fine(no crust) and my engine light has started coming on but no codes, scanner does not registar that its even hooked up so i guess wire chasing is what needs to be done unless there is anyone who has had this and has a fix

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I just tried to do the jumper wire on the obd 1 access point and no flashing codes either

With a jumper, you ought to at a minimum get the flashing *1 *2 of the check engine light, indicating the ECM is at least operating.  Are you positive the ECM is getting 12 volts?

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The vehicle is a '94, it's OBD1.5, the paperclip/jumper will not function. You're going to find that not every scanner will access the PCM as the necessary software/cable is required.

 

There is another thread on a similar issue with another 94 model.

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Unplugged iac wont run and throttle body is closed still have to check grounds at a glance they all look fine(no crust) and my engine light has started coming on but no codes, scanner does not registar that its even hooked up so i guess wire chasing is what needs to be done unless there is anyone who has had this and has a fix

The PCM has set a code because the IAC was disconnected while the ignition was on, that is normal, seeing as the car is an OBD 1.5 you're going to need a scanner that can read this particular series of electronics. The IAC code should be a DTC-35.

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It goes to our local gm dealer they say they will scan it for me on tuesday i did a little digging on this obd1.5 wow what a nightmare for the diy on a budget guy if i would have known about this i would have hunted a 92 or93 when i was lookin for my car lol

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  • 2 weeks later...

Not sure but does the 94 3.1's have the same issues with the lower intake manifold gasket leaking?

Sounds very similar to what my 91 Olds Cutlass Supreme 3.1 was doing before i replaced the LIM gasket. Mine never threw codes either.

Did you also look at the EGR?

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  • 2 weeks later...

this does not seem like proof it was the TPS. the problem was there before u put in that one. 

 

He said he was taking it to a dealer, so the TPS diagnosis is probably correct. It's not that uncommon for them to cause rpm surges intermittently when they start to fail.

 

@ Cparkes Foo - The OBD 1.5 thing isn't that big of a deal, there are plenty of old scan tools floating for a reasonable price that will read it. If you need suggestions for one, let me know.

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