odd behavior at idle

[MMAFIGHTER121]

No matter if the car is warm or cold, when I start the car it has a strange behavior problem. At first it idles fine, and will idle for about 2 minutes, if I leave it in park or drive it for a few feet then put in park again, eventually the idle wil drop lower and lower until it really starts to chug and stumble, it will do that for about 30 seconds then the idle will go too high, but be smooth, and then slowly drop back down until its idling normally. The whole process takes about 5 minutes. Now, if I don't let my car sit at idle for that long, I never experience an idle issues at all. If I shift it into gear at any point during this odd rev cycle, I don't have any idle issues either. There's no problem with driveability at all. I still have an old p0420 I gave up chasing months ago, but other than that no new codes. I still have an odd TCC locking and unlocking that will rear its head every few thousand miles, and my cruise control still won't engage. I'm hoping this might lead to a solution finally because I've tested just about everything on this car.

Edit: the idle doesn't drop before it begins to stumble. It just starts chugging worse and worse then rights itself.

 

[fudge12]

I'm having a problem similar to this, but its still present during drive cycles until the car is restarted. Two mechanic shops recommended a tune up, maybe that's what you're also in need of too. Also, are you using regular or premium gas? I started having this issue after using regular gas from a Hess gas station. I'm just waiting for my tank to empty out and fill with premium gas from BP. As per your cruise control maybe your clockspring or servo? I never got the light for the cruise control to even show up on my dash.

 

[joegr]

Next time it is doing this, tap on the IAC with a small hammer and see if that changes things.

 

[hite337]

I got the 0420 code the other day. It just happened once so I switched my o2 sensors around to see if it comes back or if its the 0430 code. This will tell me if its the sensor or the cat. So far no more CEL, time will tell. We have the same cats so I'm starting to think they were not a great idea. I am going to check the cats out soon, I still have a band clamp holding my exhaust together just past the cats. I will take the exhaust apart and use my bore scope to inspect the cats just to satisfy my curiosity. I will let you know what I find.

Meanwhile, check your IAC

 

[tireman]

check IAC sensor

remove IAC valve from throttle body, look inside holes, use carb cleaner to cleanout portals until clean. These IAC get carboned up. They respond well to cleaning. if its getting to be old, then time for a change, check ebay $30

 

[MMAFIGHTER121]

I'm beginning to suspect these cats too, but the reason I replaced them when doing the exhaust to begin with was I was getting this code before too... the clockspring has been replaced so I am believing these are all somehow intertwined.

 

[Broseph]

I haven't had any issues with the cats yet, just a lean condition on one bank that seems to be the result of some improper torque of the exhaust bolts by the shop. After fixing, so far all is normal after a month

Did you fix the strange idle? Every once in a while my idle will act erratic when I hit the gas. Mainly when the engine is cold it will idle high for a few seconds longer than normal before dropping back down. I'm thinking IAC issue but could be normal operation at cooler temps.

 

[jrand]

I haven't had any issues with the cats yet, just a lean condition on one bank that seems to be the result of some improper torque of the exhaust bolts by the shop. After fixing, so far all is normal after a month

Did you fix the strange idle? Every once in a while my idle will act erratic when I hit the gas. Mainly when the engine is cold it will idle high for a few seconds longer than normal before dropping back down. I'm thinking IAC issue but could be normal operation at cooler temps.

just curious, which bolts caused the code?

 

[jrand]

i had a weird idle for a day or two when it was a bit colder.. cleaned MAF/throttle body and ran bottle of lucas thru and it went away.

issue reappeared when i had the low fuel light come on and didnt have time to stop.. when it was almost out of fuel and i had time to stop the station i stopped at was selling premium for 60 cents more/gallon than regular.. so i put a gallon of regular in and went to the next station and vehicle exhibited rough idle plus light misfire the next time i had a cold start.

IAC is on my to do list.

paid 3cent less per gallon for the premium than i did for the gallon of regular for what its worth.

 

[Broseph]

just curious, which bolts caused the code?

They were the bolts at the flange between the manifold and beginning of the exhaust system. When the gasket there went bad it made an obvious puttering sound. After the repair I had loose clamps after the cats that I tightened up and happened to check them all.

Oddly enough I couldnt hear an exhaust leak but fresh ait mustve been getting through to throw the code

 

[Broseph]

just curious, which bolts caused the code?

They were the bolts at the flange between the manifold and beginning of the exhaust system. When the gasket there went bad it made an obvious puttering sound. After the repair I had loose clamps after the cats that I tightened up and happened to check them all.

Oddly enough I couldnt hear an exhaust leak but fresh air mustve been getting through to throw the code