Rough Idle

[jbyler]

Sparky_69 (and Bigbertha78) - my 2003 Denali is at around 500rpm at idle and as you wrote, also gets worse if the a/c is on. When I press on the gas pedal, it sputters a little and lurches and sometimes feels like it's going to die, which has me thinking maybe it is fuel line/related... I'll keep you posted...the shop will have my car until Friday and fix that...and the actuator for the a/c (had a leak in a line and already had that fixed a month or two ago and refilled/recharged the fluid...but the cold air was still failing regularly and I'd get good air pressure blowing, but it would be warm and humid, instead of cold air. I told the first shop I went to it was the actuator and they disagreed... They fixed a leak I didn't know I had, but this new shop is dialing it in with the actuator door so that I don't turn into Godzilla when the hot air starts blowing when I have the a/c on... lol Stay tuned for more info...

 

[Bigbertha78]

So since returning on the 8th of November, I had the rough idle at that moment after driving 941 miles. Since then it has just being driving rough. Swapped out the spark plug wires and plugs, also the fuel filter. Rides like a champ now so hopefully that was the problem. Plugs looked ok but they looked to be gap'd around 60 so it was possible they were original plugs. I'll let you know if there are any other issues.

 

[retiredsparky]

Smart idea to do the filter and plugs. Basic maintenance is not out of fashion yet!

 

[Bigbertha78]

So truck has been running great since I last reported after changing the spark plugs, wires and fuel filter. Drove less than a mile from the house and it's back, as soon as I came to a stop sign the RPMs go down to 300 and the truck shakes a bit hit the gas does fine then pull into drive way and as soon as I let off the gas it does it again. Turned truck off went inside for a few minutes, went back out cranked it up and it would idle at 400 in park, reverse RPMs dropped to 323, neutral was back to fine, drive was back down to 323 RPMs, took it around the block and seems to back to normal. No codes and everything on OBD2 reader seems fine. Any ideas!

 

[Jimmy John]

Have you tried pulling vacuum line off the fuel pressure regulater?

 

[Bigbertha78]

Jimmy John, I did try pulling the line off and everything was dry, no fuel at all.

 

[Larryjb]

Can you borrow a scantool that will look up the miss history?

I'm pretty new to the 5.3L Tahoe. Do they have an idle air control valve to control the air intake at idle? My Mercury has one, and when it fails it usually causes the car to stall when stopped in drive. A leaky fuel pressure regulator also has caused similar symptoms. If you pull the vacuum hose off the regulator, if you smell any fuel at all, replace the regulator. (It can be dry, but still leak fuel).

 

[Bigbertha78]

I do have a scan tool, and the truck does have an IAC valve, it is riveted on to the passenger side of the throttle body. Had the truck hooked up while it was doing the low idle but didn't notice anything other than the RPM's dropping, should I be looking at something else? I have just recently cleaned the throttle body including spraying out the IAC valve and MAF sensor. I just pulled the vacuum hose off again and it is dry with no smell of fuel.

 

[Madgrty]

If it ever says "REDUCED ENGINE POWER" i know our electronic throttle bodies will sometimes fail and replacing them can fix the issue...

 

[Bigbertha78]

I would love to have some type of code or anything to at least help me!