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Idleling Problems


cardude43

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My '92 GP has a 3.4 and is having idleing problems again! :verymad: Last November it did this and my mechanic said the throttle body was gunked up, so he cleaned it. Until now it had no problems and I haven't put more than 3,000 miles on the car. Okay so this is what it is doing: S.E.S. light is on; when it is in P it idles about 1,500 rpm; when it is in R it idles about 1,100 rpm; when it is N it idles about 1,500 rpm; when in OD it idles around 1,250 rpm. So, what the hell is the problem! I'm not sure whether my mechanic is right or if it's something else. Please help

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First, get the code of that SES light and find out which component might be failing or bad.

 

Well, the throttle body could be gunked up again. I would do an IDLE Re-Learn as well and see if that makes a difference.

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I can almost guarantee that the code you will get is 35.

 

The ECM always has a DESIRED IDLE speed, and code 35 will set if the actual RPMs are 200 above or below this DESIRED speed for 50 seconds.

 

Before you run out and change the IAC Valve, make sure you do some actual diagnostic checks first...

 

Code 35 is one of those where it could be like 8 or 10 different things...

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I also own a 3.4L. I wouldn't say that those RPM's are too erratic. A little bit high maybe, but so long as it is not wavering up in down when in a given gear I don't think this is overly bad. I've heard of some DOHC owners consistently idling above 1500 rpm (I idle around 1000). I would do another throttle body clean. Also, when you're done this unscrew the IAC and wipe of the tip of it (it is probably black and gunky), and use a screwdriver and rag soaked with TB cleaner in the passageway that you pull it out of.

Jeff

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It is wavering up and down in all gears. :?

 

Sounds like the IAC is all gunked up.

 

Devilsdawg, I think you meant the MAT/IAT sensor, never heard of a AIS. :wink:

 

Robby

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Air Temperature Sensor

 

Common Names:

Manifold Air Temperature Sensor (MAT)

Air Charge Temperature Sensor (ACT)

Inlet Air Temperature Sensor (IAT)

Throttle Body Temperature Sensor (TBT)

Vane Air Temperature Sensor (VAT)

 

He might meant AIS as Automatic Idle Speed sensor (AIS) OR Idle Air Control sensor (IAC).

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Air Temperature Sensor

 

Common Names:

Manifold Air Temperature Sensor (MAT)

Air Charge Temperature Sensor (ACT)

Inlet Air Temperature Sensor (IAT)

Throttle Body Temperature Sensor (TBT)

Vane Air Temperature Sensor (VAT)

 

He might meant AIS as Automatic Idle Speed sensor (AIS) OR Idle Air Control sensor (IAC).

 

Yeah, I was just picking nits with him

 

Robby

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If your RPM's are fluttering up and down when in a gear I would say there is a pretty good chance that you have an intake gasket leak. Not terribly fun to do on the DOHC, but gives you a chance to do some other little things while you are in there (like fuel injector o-rings, JB Welding the distributor o-ring, changing the coolant o-ring, etc). If you haven't thrown an IAC or TPS (though a bad TPS will certainly do this) code then these probably aren't the overriding source of the problem.

To check for the intake leak spray TB cleaner around the sealing surface. If engine RPM's change you've got a leak.

Also, check all vacuum connections; the little t-shaped bugger below the EGR Valve and adjacent to its pipe has been known to pop off. It is tough to squeeze your hand back there between the plenum and the firewall, but with patience it can be done.

Jeff

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