Rough Idle in cold weather


wagslick
12-10-2010, 07:16 PM
I have a 99 Silverado Z71 ext cab with 5.3L engine. The truck starts fine in cold weather but then after about 30 seconds of running smoothly the truck begins to rev. The RPM's jump up and down from 500 to 1500. When I accelerate or drive, the problem goes away. Then when at a red light, the truck begins to rev again and the lights get dim, then get bright. If I don't have the brake fully depressed the truck lurches forward a couple inches each rev. This doesn't happen in the summer, only in the winter. Any ideas?

4x4junkie
12-10-2010, 11:19 PM
this sounds like a sensor problem on the emissions control system, I would start by have the codes read on the vehicle, if none are shown I would check the electrical connections for the following sensors, map sensors, maf sensor, throttle position sensor, fuel pressure regulator, and the air temp sensor. if you have a haynes or chilton manual it shoud explain location and give specifications and information for checking them all.

j cAT
12-11-2010, 09:37 AM
I have a 99 Silverado Z71 ext cab with 5.3L engine. The truck starts fine in cold weather but then after about 30 seconds of running smoothly the truck begins to rev. The RPM's jump up and down from 500 to 1500. When I accelerate or drive, the problem goes away. Then when at a red light, the truck begins to rev again and the lights get dim, then get bright. If I don't have the brake fully depressed the truck lurches forward a couple inches each rev. This doesn't happen in the summer, only in the winter. Any ideas?

the dimming of the lights indicates the alternator or the wiring/connectors /grounds need cleaning and inspection..

battery leads/ground wires to frame engine/ feed wires ..

measure voltage at alternator terminal using the alternator frame as the ground. rev engine should not vary ..when 32deg f cold start should be 14.75volts ..when engine is fully at normal temp volts should be very close to 14.25volts..

you did not mention DTC/check engine light so start with the above tests/inspection !

PAT GOL
12-16-2010, 09:37 PM
had this problem with my 2001, inside the throdle body at the butterfly had gummed up with some sludge clean it up should run fine

wagslick
12-19-2010, 01:00 PM
had this problem with my 2001, inside the throdle body at the butterfly had gummed up with some sludge clean it up should run fine

Good vid on cleaning throttle body.

wagslick
12-22-2010, 03:09 PM
had this problem with my 2001, inside the throdle body at the butterfly had gummed up with some sludge clean it up should run fine

I got a can of throttle body cleaner, removed the air intake and sprayed that stuff around the throttle body. I could see a bit of gunk come off. I opened the butterfly and tried to clean up some stuff behind it with a paper towel and it came out black. The truck sputtered a bit when I started it but it has a low consistent idle just like it should. PROBLEM FIXED. Great advice PAT GOL.

MikeD266
12-22-2010, 07:10 PM
From my own cleaning experience on my 99 the truck WILL sputter a bit due to the combined removal of the air intake and the crap and cleaner in the combustion mix. Should blow out in a minute.

If things are that cruddy in there you may want to consider taking an old toothbrush to the TB interior for a minute or two after spraying with cleaner and see how well things get cleaned out.

Just my .02

j cAT
12-22-2010, 08:33 PM
From my own cleaning experience on my 99 the truck WILL sputter a bit due to the combined removal of the air intake and the crap and cleaner in the combustion mix. Should blow out in a minute.

If things are that cruddy in there you may want to consider taking an old toothbrush to the TB interior for a minute or two after spraying with cleaner and see how well things get cleaned out.

Just my .02


the IAC mounted on the side of the throttle body maintains the rpms..this part requires removal and cleaning every 20-30 ,ooomi..

using a tooth brush and throttlebody cleAner clean the seat [pindle] and also the bore that this part sets into..,

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