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Need feedback.. rough idle and hesitation once engines is hot, no codes on DIC.

Big2dabank

Well-Known Member
Messages
1,216
Location
Central Florida
Hopefully someone else has experienced this problem. I have a 2005 H2 SUT with 200,000 miles and over the past couple of months, I have noticed that there is slight hesitation on acceleration and the idle is very rough once the engine is hot or has been running for more than 30 mins. It feels almost like a misfire, but the DIC is not showing and codes and had a diagnostic done yesterday and it did not show any codes, and all sensors (i.e., O2, knock, etc.) were showing fine. The technician I spoke with is someone I trust and is a personal friend, he told me that it is most likely the timing chain, which may have stretched slightly and when the engine is cold the chain is tight enough not to notice the problem, but once the chain gets hot, it is possible that even some minor expansion could cause enough slack in the chain to throw of the timing. It seem logical, but I wanted to see if anyone had any other ideas before I go this route. For starters he suggested I put a wrench on the drive fan and try to turn the crank shaft to see if there is any noticeable movement or play when the engine is cold and to try this again when the engine is hot to see if it develops any play in the chain. Any thoughts you guys may have would be appreciated.
 

cgalpha08

"Like Nothing Else"
Messages
3,584
Location
Indianapolis, IN
My first thought, before I read it, was the timing chain. Reason being at 200k miles it would make sense as a part to adjust or replace (not sure if you've done this or not). Just my .02 :)
 

SuperBuickGuy

Well-Known Member
Messages
3,403
Location
Woodinville, WA
I'm not going to say it's impossible that the chain stretches when it's hot, but it's impossible....

That said, it could be one of the tensioners that causes the problem. What does the running graphs show while you're running? Is the EGTs getting too hot or too cold? how is the timing? you can record with HPTuners then play back what it is... since it's doing it often, you should be able to capture what the issue is. I had a similar issue with my H3, eventually I got the trouble code of the gas pedal and/or the throttle body. Until I got a code, it was pretty frustrating. I'm not suggesting replacing those parts - I'm simply saying that sometimes you have to wait it to throw a code (presuming you can't diagnose it with a running test).
 

Big2dabank

Well-Known Member
Messages
1,216
Location
Central Florida
He didn't mean stretch in the conventional way, so I might have misstated that part. He meant that the pins in the chain become worn, thus creating slack, which could worsen as the engine heats up and why my problem is not noticeable when cold and only after it heats up. This one is certainly a little strange for me, I never had to deal with a timing chain issue before. We tried everything yesterday to try to get it to throw a code, and it never would, almost got it stall several times with a quick bump and release of the skinny pedal. I am going to let my friend drive it for the evening and data log it to see whats going on.
 

DaveK

Well-Known Member
Messages
67
Location
So Cal
Don't know if this will help, but I thought it's worth a try:

Document ID# 1527156 2003 HUMMER H2

Idle Instability, Low or Rough Idle with Electronic Throttle Control (Clean Throttle Body) #04-06-04-040 - (06/14/2004)Idle Instability, Low or Rough Idle with Electronic Throttle Control (Clean Throttle Body)

2002-2003 Cadillac Escalade, Escalade EXT
2000-2003 Chevrolet Silverado, Suburban, Tahoe
2002-2003 Chevrolet Avalanche
2000-2003 GMC Sierra, Yukon, Yukon XL
2003 Hummer H2

with 4.8L, 5.3L or 6.0L V8 Engine (VINs V, T, Z, N, U - RPOs LR4, LM7, L59, LQ9, LQ4) and Electronic Throttle Control

Condition

Some owners may comment on an idle instability, low idle speed or rough idle.

Cause

Condition may be caused by deposits in the throttle body bore.

Correction

Clean throttle body bore and throttle valve plate of carbon using a shop rag and an appropriate cleaner. Refer to Engine Controls Repair Procedures - Throttle Body Cleaning Procedure. This procedure may be performed at any mileage necessary. Check to determine if the PCM calibration has been previously updated to one that includes the update for throttle body coking.
 

BeastOfaTruck

Member
Messages
8
Location
Idaho
Could be bad IAC or crank sensor, could have something going on with MAF, but they generally throw codes. It hasn't died on you yet, has it? None of these would throw a code unless it died.
 

Big2dabank

Well-Known Member
Messages
1,216
Location
Central Florida
Could be bad IAC or crank sensor, could have something going on with MAF, but they generally throw codes. It hasn't died on you yet, has it? None of these would throw a code unless it died.

MAF and throttle body are clean, that was the first thing I did. Truck has never stalled on me, when I was having the problem, I could rev the engine in park and get it close to stall, but it would never actually stall. Now thats its cols here in Florida I can't get the problem to manifest itself, so it has to be heat related somehow.

Hey Big2Bank, did this problem ever show itself? Did you figure anything out with it?

Not yet, now that we are getting some cold weather here in Florida it has not been noticeable. I do notice a slight power loss overall and the truck feels sluggish in general, but not the intermittent problem I was having when the truck gets hot. I'm gonna wait until the weather warms up again to start getting a consistent problem when the truck gets hot. Then will finish diagnosing it.
 

5gn-h3t

Well-Known Member
Messages
616
Location
Northeast Pennsyltucky
Could be misfiring but not enough to throw a code. See if your friend can read the misfires live on a scan tool. Figure out what cylinders have the highest misfire and go from there. Swap easy stuff like coil packs, injectors, etc and see if it moves. Could be anything from an almost-bad electronic part to a flat cam.
 
Messages
6
Location
Colorado
Change spark plugs if you haven’t and get a catch can. If there is oil in your intake box or tube you need a catch can for the positive crankcase ventilation. Clean the throttle position sensor on the throttle body with MAF sensor cleaner and do a pcm relearn procedure.
 

Big2dabank

Well-Known Member
Messages
1,216
Location
Central Florida
Damn I don't even remember what we did to fix this one it was so long ago. I think it was something really simple. Trucks running great almost 4 years later.
 
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