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Rough idle and hesitation when accelerating

M

Macc

Full Member
Joined
Jan 20, 2013
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26
I have an 02 Avalanche 2500 with 198,000 miles. It’s had a rough idle for a while now and also some problems when accelerating. The rough idle is constant. You can hear it and also feel it when you sit in it. The tach needle doesn’t move at all from what I can tell. Now to the hesitation. Throttle response has been really bad if I try to give it any kind of a push, like going up hill, it falls on it’s face and struggles to pick up speed. It doesn’t just do it at freeway speeds it does the same thing from a stop or slow roll. If I’m real light on the gas it will go pretty good. I noticed it responds better in the morning vs the afternoon but not perfect. These are some of the things I have done so far. In the past 2 years I replaced 4 o2 sensors, replaced the fuel filter, and I cleaned the mass air flow sensor. The fuel pump was also replaced about 3-4 years ago along with a tune up. None of these had any impact on either problems. Last month I replaced all ignition coils and that made a huge difference I finally had some power back. But the rough idle is still there and it is still hesitating. It doesn’t fall on its face anymore but I can feel some resistance still but the power pushes through it. Mornings seem to be better then afternoons but it’s still there. I put my scanner on it but no codes show up. Is there anything else i should be looking at?
 
Have you cleaned the throttle body?
 
I once ran into a rough idle and power hesitiaton situation exactly as you described. Eventually started having random codes related to the throttle position sensor as well as some others. I ended up cleaning the MAF sensor and the throttle body. Nope. Replaced the throttle position sensor assembly. Nope, didn't really help. Things got worse and I eventually replaced the whole throttle body. Still had issues. Eventually started getting misfire codes. I was baffled. Then one day I discovered one of my spark plug coils had popped slightly loose. Pushed it into place and wham, problem resolved. Or so I thought... over the next few weeks the problem came back. Turned out that the loose coil was 'off' long enough that it destroyed that one spark plug. After replacing the plug (went ahead and replaced that coil too) it's been running puuuurfect ever since. So if you haven't already, check out your spark plugs. Could have a faulty one that isn't throwing misfire codes.
 
ca2kjet said:
I once ran into a rough idle and power hesitiaton situation exactly as you described. Eventually started having random codes related to the throttle position sensor as well as some others. I ended up cleaning the MAF sensor and the throttle body. Nope. Replaced the throttle position sensor assembly. Nope, didn't really help. Things got worse and I eventually replaced the whole throttle body. Still had issues. Eventually started getting misfire codes. I was baffled. Then one day I discovered one of my spark plug coils had popped slightly loose. Pushed it into place and wham, problem resolved. Or so I thought... over the next few weeks the problem came back. Turned out that the loose coil was 'off' long enough that it destroyed that one spark plug. After replacing the plug (went ahead and replaced that coil too) it's been running puuuurfect ever since. So if you haven't already, check out your spark plugs. Could have a faulty one that isn't throwing misfire codes.
Click to expand...
Man that would be an easy fix if that’s the case. Thanks I’ll give them a check tomorrow along with cleaning the throttle body. Hopefully that will do the trick
 
Thanks for all the suggestions. Work has been pretty busy I haven’t had a chance to check things out. Hopefully Saturday I’ll be able to spend some time on it
 
Update. I got off work early today so I cleaned the throttle body and pulled the plugs and inspected them. Visually it didn’t seem like the throttle body got that much cleaner but I sprayed in there pretty liberally and wiped the areas I could reach. One question. Is the butterfly supposed to close all the way? Mine seems to be open a little bit on the top, I can push the bottom and get it to close completely.
As for the spark plugs they all look good. They had a small amount of ash deposits on all of them. I noticed one of the boots wasn’t all the way on the spark plug so I went around and made sure they were all on good.
After all that I took it for a test drive and everything seems to be good. The rough idle is gone and so is the hesitation. A few more days of driving just to make sure but I think all the problems have been solved.
Thanks for all the suggestions! I’m so glad to have it running good again I love driving this truck.
 
On more thing to do is use some fuel cleaner stuff in bottle once and a while.
Cleans tank fuel gage pick up and cleans injectors a tiny bit...

The seafoam treatment works too.... but little more time is involved.
 
ygmn said:
On more thing to do is use some fuel cleaner stuff in bottle once and a while.
Cleans tank fuel gage pick up and cleans injectors a tiny bit...

The seafoam treatment works too.... but little more time is involved.
Click to expand...
Thanks I’ll pick some up
 
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