: Weird Idle Issues



blunted
02-09-06, 12:59 PM
Sup guys.. for a while now my Eldorado will idle at 500-550 RPM, no complaints there, very smooth. However , about every 2-3 minutes the rpms will suck down to about 400 rpm and make a rumble sound.. sounds just like if the engine hiccuped really really hard. I've done a complete tune up.. wires, plugs, all new coils, fuel filter.. all that good stuff. I cant figure out what could possibly going on, and its really bothering me. Any insight is very appreciated, Thanks!

mcowden
02-09-06, 02:24 PM
Sup guys.. for a while now my Eldorado will idle at 500-550 RPM, no complaints there, very smooth. However , about every 2-3 minutes the rpms will suck down to about 400 rpm and make a rumble sound.. sounds just like if the engine hiccuped really really hard. I've done a complete tune up.. wires, plugs, all new coils, fuel filter.. all that good stuff. I cant figure out what could possibly going on, and its really bothering me. Any insight is very appreciated, Thanks!

Sounds like a possible Idle Air Control valve issue or a dirty throttle body bore and blade. Have you cleaned the TB lately?

CadillacSTS42005
02-09-06, 02:31 PM
is this during the cold only?

blunted
02-09-06, 02:50 PM
It happens hot usually.. when its cold the rpms stay at around 750 until it warms up, then they drop down to 500 and if i just sit there idling it'll do the hiccup. Also, no I have not cleaned the TB.. I have however run Chevron Techron fuel system cleaner thru it and mostly use Sunoco 94.

mcowden
02-09-06, 04:53 PM
It happens hot usually.. when its cold the rpms stay at around 750 until it warms up, then they drop down to 500 and if i just sit there idling it'll do the hiccup. Also, no I have not cleaned the TB.. I have however run Chevron Techron fuel system cleaner thru it and mostly use Sunoco 94.

Gas and injector cleaner won't do anything for the throttle body. The TB is subject to crud from the PCV system and any particulates remaining in the intake air after the filter. It needs to be cleaned every so often. If you have a sticky throttle pedal, that's a sign the TB needs cleaning. There are holes on both sides of the throttle blade for the IAC bypass valve. Clean into those holes as much as you can. Use either a carb cleaner or throttle body cleaner to do the cleaning. Just scrub up both sides of the blade and the bore as far into the TB as you can reach. Everybody thinks Seafoam is a wonder fluid, but I don't think it works worth a crap for this job. Carb cleaner or TB cleaners work much better.

blunted
02-09-06, 05:39 PM
Thanks for the advice, the only thing that bothers me is that its soo smooth and then bam its does the harsh hiccup.. like if the engine chokes or something. I would think a very dirty TB would cause a more constant problem. I did some research and it seems like 500-550 is a kinda low idle, could it be that when it misses like that its cause its idling a little too low and comes near dying?

molotovman5000
02-09-06, 11:37 PM
sorry for the thread jacking, but whats normal idle? mine idles at 650-700

94greencaddysls
02-10-06, 01:14 AM
i want to say 575

mcowden
02-10-06, 12:07 PM
650 is normal idle. If cleaning the IAC and TB doesn't help, the IAC may be in need of replacement. It could also be something like an AC compressor switch. Have you checked for codes yet? Check those and post them here.

Ranger
02-11-06, 09:49 AM
What year engine is this?

blunted
02-13-06, 12:03 AM
Its a 94 Northstar.. 76300 miles

auroradude
02-13-06, 01:00 AM
egr valve. mine idled about 2k rpm all the time in the summer until it stalled when i was going 70. Mine was right around that kind of mileage too. Either clean it or replace it.

I hated putting it into gear when it did that too. Its like neutral slamming it.

peteski
02-13-06, 02:53 AM
Did you pull any codes from the PCM? Maybe there will be a clue...

And you're corect - 550 is low. Normal idle is 700-750 RPM.

Peteski