My car idles like 1.2 to 1.5K rpm when i first start her then she goes to 1000 to 990 rpm when warm. So thinking a throttle body is like a carb i find the idle adjust screw and turn it and .. nothing umm how can i lower this to a healty idle? Thanks

 

mess with the TPS (throttle position sensor) or the IAC (idle air control) both are possible culprits of your problems.

 

If it is a V6, the TPS is self adjustable and cannot be adjusted manually. Well, on my 91 3.1 anyways. Make sure you have no vacuum leaks first, if not look into replacing your IAC and possibly your tps.

 

Believe it or not, I've had a vaccum leak though the intake gasket before that caused it to always idle at 1200 rpm's. What fun that was.

So, I would check for vaccum leaks (yet any big ones like a power booster would more than likely stall the engine if I remember right).

 

2.8's came with an adjustable TPS....the 3.1's had a non-adjustable type. Just clearing that up.

Skatepunk...It isn't hunting for an idle or surging is it?

 

I believe the other guys are on the right track, but here's some other reasons. 1, the low pressure switch on the power steering system is faulty, and is stuck closed. This switch raises the engine's idle when an excessive load is placed on the power steering pump... such as, doing a k-turn in a parking lot. 2, if it's an automatic, the park/neutral switch is acting up. The p/n switch raises the engine's idle when the trans is put in gear. If the switch is faulty and it "thinks" you're in gear when you're really in park or neutral, the switch would tell the engine to rev higher.

AH! Your signature line says B&M shifter? Who installed it? There's a right way to wire up the shifter and a wrong way. The wrong way doesn't take care of the high idle problem. The correct way involves using a Radio Shack relay (wiring directions are with the shifter), and that properly eliminates the factory p/n switch, and lowers the engine idle when in park or neutral.

 

n/m, double post

 

IIRC, its supposed to idle like at 1200rpm when you first start it up, after about 30 secs it goes down to normal. Is this what yours does? if so, its supposed to do that.

Put your car in gear, and see what the idle goes down to, it should be 900 IN GEAR, not in park or neutral, which is a common mistake people make.

 

Tom you may be onto something... I highly doubt a vac leak cause i just changed all the plenum gaskets this weekend and it idled the same before and after the change. BUT there was a point where she would stall everytime i cut the wheel fully. Could you show me where that sensor is?

As for the shifter .. I installed it. It had the same idle problem with the stock shifter. In Park or neutral the idle raises a bit and in gear the idle lowers a bit but its still high

 

given the changes you've already made, i'm sure you already knew what im about to say. But on the back of the throttle body in a small hole on the top driver's side is a small torx screw, by loosening or tightening this screw, the butterfly will open or close more or less which will also cause the engine's idle to change...maybe someone bumped that a long time ago, and it simply hasn't been reset

 

Skatepunk, did you wire in the relay to the B&M's switches?

The sensor is located in the hard line coming from the power steering pump; you can't miss it. It's a two-wire sensor. To check for failure, you turn the steering wheel all the way against the stop; the car should rev up. I can't recall if the switch opens or closes under high pressure; I think it closes, but don't quote me as being 100% accurate on it. So you could test it with an ohmmeter, too.

 

To add to that...if there is no cap covering the idle stop screw, then the idle has more than likely been messed with in the past. GM puts a metal cap over the screw ends to make it a royal pain in the *** for anybody to adjust them. I guess they do that to keep people from upping their idles to mask engine/sensor problems so they actually have to REPLACE the bad parts.

 

Yeah there was no metal cap over the idle adjust .. just stuck a T15 bit and turned but when i turned it back the screw just went back not the throtlle linkage. Maybe the cruise control is holding it?

Tom the relay is wired w/ the switches .. reverse lights work fine and idle raises to 1.2K in park and neutral. Im gonna check that power steering pump out tommrow Thanks

 

Hey guys i think i solved it .. i used my Chiltons for the steps to reset the IAC and now she idles 1.2-1.5K upon startup (warmup) then about 900 in park and about 600 in gear

 

Cool! Thanks for telling us how you fixed it! (And glad to hear that you wired up the relay and did it the right way! )

 

Heh thanks .. idle went up a little but fooling with the idle screw worked.