low idle rpm only about 300-400 and won't rev over 1100 in park

[godfearingman]

Hi what causes low idle speeds? And not revving over 1100 RPM in park but will do about 4000 in drive. I think the throttle cable is stretched and the trans is on it's way out anytime now would one or both of them cause the issues? Or could be a bad sensor? Or plug wires, distributor itself the cap or rotor? The ignition coil? Plugs which I replaced myself when I bought the car don't have more than 10-15 miles if that. The cap and rotor and wires all look relatively new. I disconnect vacuum lines and nothing changed. Thanks in advance

 

[Jgehret]

What year? Engine? Trans? Mods? Did you pull codes?

 

[godfearingman]

94 GT 302/5.0 stock motor and transmission wise I think. Only mods I know are x pipe and magnaflow mufflers I can pull codes again the cel comes off and on. I bought the car about 2 months ago to fix up myself since I couldn't afford to buy a nice running and driving one without any issues.

 

[Jgehret]

First remove and either clean your IAC (idle air controller). Secondly, clean your MAF. Then follow the steps in the photo. Let me know what happens from there

 

[godfearingman]

I'll need an new gasket for the IAC won't I? As far the MAF sensor it looks clean and basically new unless I need to unbolt the black box from it to clean it which I don't have the special bit need for the torx screws

 

[87hurricane]

Most times you can reuse the gasket from the iac. As for the MAF, you'll probably want to remove it from the housing to clean it properly. Be careful when you take it out, as the wires on the end are fairly fragile, dropping it would probably kill it.

 

[87hurricane]

BTW, I think there is a rev limiter in park or neutral, so that part is probably normal.

 

[Jgehret]

You can buy the security torx bit kit at harbor freight for something like $10

 

[godfearingman]

well the whole assembly for the MAF sensor and black part that mounts in to it look like there new. I took off the IAC valve what do I clean it with it? Carb or brake cleaner? It's dark brown or is that normal?

 

[toyman]

BTW, I think there is a rev limiter in park or neutral, so that part is probably normal.

There is no rev limiter.

 

[CC'S95GT]

Use MAF cleaner or electronics to clean the MAF. Carb and brake cleaners will leave a residue.

 

[godfearingman]

The MAF assembly looks brand new no carbon or anything anywhere the IAC valve is brownish black inside though. I stripped out the head of the screw on the TPS taking it off hoping Oreilly's or some other parts store will have another bolt I can use to replace it or should I go to Lowe's? Heard other's say they have similar bolts as well.

 

[87hurricane]

If you have a local ace store they will probably have a better selection of bolts and screws than a parts store and probably more than Lowes too.

 

[godfearingman]

the only way I can test the IAC or TPS is to use a multimeter right?

 

[87hurricane]

It's easy to check the tps with a multimeter, not so easy to check the iac that way. If you think the iac is bad, just replace it. That being said, I don't think your iac is bad, normally they will cause hanging idle conditions, not lack of idle, and they definitely won't keep the car from revving up.

 

[87hurricane]

When you check your tps, check the voltage with the throttle closed, and then watch for a smooth increase in voltage as you open the throttle, if it doesn't change, or it jumps drastically, then that is your problem.

 

[godfearingman]

I'll get some throttle body cleaner and clean the iac and maf real good and borrow my step dads multimeter to test the tps. What would I set the multimeter to?

 

[87hurricane]

DC volts. There are three wires coming out of the tps, a ground, 5v ref, and the tp voltage. You want the ground and tp volt wires, should be gray/white and gray/red according to my wiring diagram. The voltage you're looking for should be somewhere around 1 volt at idle, and it should increase as you open the throttle. If you get 5volts you're on the wrong wire.

 

[godfearingman]

Do I need to have the car running and up to normal temp?

 

[87hurricane]

You should be able to check the voltage without the car running but the key on, or with the car idling, the reading should be the same, or at least very very close.