• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

2000 Grand Prix, high idle or normal?

Interesting behavior

So i went out i the morning and started my car and it was really cold, around 20F maybe and it idle's lower when its cold 1200-1300RPMs and around 1700 when it was 50 60F+ This dont make no sense🤔
 


Re: Interesting behavior

GT2000 said:
So i went out i the morning and started my car and it was really cold, around 20F maybe and it idle's lower when its cold 1200-1300RPMs and around 1700 when it was 50 60F+ This dont make no sense🤔
Click to expand...

I'd be suspicious of an intake vacuum leak that is keeping the idle high due to un-metered air entering the intake. Perhaps you've already checked that, but one of the simple ways to check for an intake leak is to introduce smoke to the intake and observe if it escapes. On the GTP I recently worked on, there was an intake gasket leak that was was found using this method. After all the issues were addressed, the engine now idles at 700-750RPM when warm, cold start idle is about 1200 RPM.
 
Well time to bring this thread back, I've let it go for awhile but i would like to fix it and also I've noticed along with this high idle, now the idle isn't steady cold or hot. It bounces 100-200 rpm randomly, Kinda bobs up and down sometimes, not sure if this is a new thing or if I just never noticed it. Also when starting warm sometimes it will do it more dramatically and then level out mostly.
 
Check the big vacuum connection on the back of the upper intake, the one the brake booster hose connects to. I had a leak there and couldn't figure it out. Pulled the connector out of the UIM and ran some RTV around it and stuck it back in and let it cure. Next day fired it up and all was well.

Other than that it still sounds like a vac leak somewhere to me. Try spraying carb cleaner while the engine is running around where the UIM meets the LIM, throttle body, injectors, any vac lines, etc. and see if you get the idle to change. If you find a spot that makes the motor idle change then that is a vac leak and needs to be fixed.
 
Did you ever try unhooking throttle and cruise cables to see if they are binding? I've seen this a few times when someone moves them slightly on the strut tower, they could get in the wrong position and cause high idle.
 
Live Data- Right after starting dead cold- load PCT 8.6, ECT 41, MAP 5.8 RPM 1334- TAC IS READING HIGHER?!, spark ADV 9.5 IAT 42, MAF 0.03, TP 0.4. Scan tool tells me 1334, gauge is reading 1600ish
 


cold start is running off the pcm settings, not the sensors yet. need to warm up then it runs off what you see as data.

when cold its gonna have a high idle, thats your choke. aka dumps fuel really.
 
The biggest thing im interested in why is my gauge reading high? I do think there is some sort of vacuum leak cause of a weird hiss/suck noise i hear with the hood open at high cold idle.
 


Also when cold started the RPM's fly up 2.5k and then go back to bout 1.5ish. Also when i turn the engine off, bout 2-3 seconds later ill here a short hhh sound, sorta like a hiss. My scan tool won't do TPS readings. Warm 700 rpm readings are MAP 4.9psi, spark adv 23.5 IAT 84, MAF 0.01
 
I unplugged my MAF sensor at idle and it didn’t change a thing, it stayed running. I thought when they are working correct the car will shut off when unplugged? When i plug it back in running engine makes a weird noise. Didnt change my idle cold though being unplugged.
 
Scottydoggs said:
you unplug the maf, then start it.
Click to expand...
Unpluging and starting didn't change much except idle was even more off and weird. Now i realized with my scan tool that the RPM gauge reads 2-300 rpm's above what the scan tool says at all times. Here is the weirdest thing. I cleared out the codes and live data today before i drove it and it drove PERFECT. No more confused transmission around 40-50 like i mentioned in another thread, no more hesitation when i would go to get on the gas a stop. The car drove amazing. This happened LAST time i cleared out the computer codes and data and soon there after it was back to its old ways. I believe the other thread was called "Odd transmission behaviors"
 
The car makes a sound under hood, like a sucking sound near the throttle body, thinking possibly the throttle body gasket or something is leaking, but for some reason i can't get the TB off the car. I took all 4 nuts off and there are two brackets, one of which looks as to if its welded to the exhaust/egr tube? Said bracket is preventing me from getting the TB off! What the heck, am i missing something?
 


You must log in or register to reply here.
Back
Top