1996 grand am high idle 5000+ rpm

[mixerman32]

I am getting crazy idle as soon as i start the car. It started after the heater core was replaced. Car ran fine before heater core was replaced by myself. When i was done and anti-freeze was filled i started the car and idle was bouncing from 3-4000 RPM right away, kind of like i was pressing and releasing throttle pedal though i wasn't. Check engine light came on and i got 2 codes 1 for TPS sensor low circuit and the other was for MAP sensor low circuit. I replaced both sensors and now i am getting a very high idle 5000 RPM and climbing. I have replaced the vacuum line at the bottom of the map sensor and one on the sensor near the A/C compressor. I am stumped on what else to look for any help would be greatly appreciated.

[xeroinfinity]

Welcome to AF !!

Did you happen to knock off any vacum lines under the dash ?
Thier is one going to the HVAC control head unit.

I'd also check that the throttle cable is not sticking causing this.

[mixerman32]

Thanks for getting back to me, I did recheck everything under the dash to make sure nothing was left unhooked and my throttle cable is not hung up. However, there was a very rich fuel odor and a lot of exhaust smoke coming from the engine compartment and the hole in the muffler when it was idling fast. After spending an hour and a half rechecking everything again I tried to start the car and it just turnes over till the battery dies, is it possible the timing belt or something just crapped out???

[xeroinfinity]

The high idle sounds like a vacum leak or the IAC is unplugged.

It could be a timing issue but it shouldnt just make the idle high more like irratice idle or back firing.

Had you checked for codes after replacing those components ??

[mixerman32]

I did check for codes after replacing sensors and nothing comes back faulty. However while trying to start the car because it won't start now,and after recharging the battery, it does backfire through the throttle body.

[xeroinfinity]

Might pull the plugs and see if they are wet/fauled out.
Check and see if you're getting good spark on all 4 plugs, if not then I'd check the coils and ICM.

[mixerman32]

Ok I did check pull each of the plugs and they did seem a little fouled/wet then i put them back in. I charged the dead battery from trying to start it yesterday and got the car started today. It ran a little rough for the first min or two then idle started gradually coming up to around 3000 RPM then I got a check engine light, code P0300 Cylinder Misfire Detected (Random). What would cause this and what should i check to fix it? Also the high RPM thing is still boggling me, could this misfire thing be contributing to the high idle? All your help is greatly appreciated-Thanks.

[doctorhrdware]

Could be bad spark plug wires, spark plugs, coil or a bad injector. More likely I would guess a bad coil.

[xeroinfinity]

I doubt the high idle is related to the misfire(s) could have just happend when trying to start it.

If you dont have any vacum leaks you should check/test the IAC.
Though being that high of idle still sounds like a bad vacuum leak.

Good Hunting!

[cboy2us]

I would have to see a cut-away of the fuel pressure regulator, but I would venture a guess that a diaphram in the regulator devoloped a hole allowing gas to flow back in through the vacuum hose causing a rough or high idle, as well as fouled plugs. I'm not sure if Grand am uses vacuum hoses on the fuel pressure regulator, but it sounds like a good possibility here. Any pointers?

[3100]

Can your scanner show live data or just codes, if yes give us readings for MAF g/s, MAP Voltage, IAC count. TPS Voltage all measured at idle. Make sure you did not bend any of the sensor terminals so that they look like they are properly connected but they are not maing any contact with the connector. this must be big vaccum leak, how about power booster vaccumm line is it connected? See at what position is your TB plate make sure it is not stuck or someting

[mixerman32]

Hey guys just an update on the Grand Am idle issues. It turns out I had a malfunctioning cruise control motor that was pulling on the throttle body causing the high idle problem. This was checked out at a repair shop nearby cause I had it after checking and rechecking EVERYTHING twice. Well it wasn't all that bad cause I did replace all vacuum hoses and a few were pretty bad anyway. Just wanted to thank everyone for all the advise, it was very helpful and any future problems I will come here for advise first again THANKS.

[j5ivek]

MIXERMAN32...Mine was doing the exact same thing, I put a new TPS throttle position sensor on it, it straightened out idling hi and low high and low. but it would still idle high at different occasions, especially when I put it back in park.

A mechanic helped me check it and the wires just about two inches before the TPS going to the clip had been black taped by the previous owner and were loose just pulled apart.

That fixed that part and ran great Idled right about 800 rpm!!!

Now it bucks and jerks and I think the fuel pump is out?

[younggm95]

my 95 idles high then low gos up and down like ur geting on and off the gas, and will stall out and take 5 to 10 mins for it to restart