C5 Stalling Until Engine is Warm
Thread Starter
Race Director
Joined: May 2000
Posts: 14,542
Likes: 5
C5 Stalling Until Engine is Warm
This problem just started with my 2000 C5 MN6 convertible (70,000 miles).
Mods:
Donaldson Filter
Open MAF ends (also happens with the stock MAF ends)
BBK 80mm TB
LS6 manifold
Corsa Indy Pace Car Exhaust
RWHP is 337 on the dyno.
Car will stall and hunt idle (especially with A/C on, and when coming to a stop -- as at a light) until temps are up (about 15 minutes of driving). No codes. Connections are tight at air bridge and MAF sensor. Stalling is less if the A/C is not on, but when you switch it on, the idle will hunt down to below 500 rpm, and/or stall.
It did not do this in the past, and the only change I can think of is a dealer GM reflash in connection with the MN6 recall. That, and the mileage. I've also tried Techron.
Oh, yes, it also seems to be running a lot more "boggy" at the low end in the higher gears (4th and up), until about 3,000 rpm plus.
Thanks for any help, suggestions.
Mods:
Donaldson Filter
Open MAF ends (also happens with the stock MAF ends)
BBK 80mm TB
LS6 manifold
Corsa Indy Pace Car Exhaust
RWHP is 337 on the dyno.
Car will stall and hunt idle (especially with A/C on, and when coming to a stop -- as at a light) until temps are up (about 15 minutes of driving). No codes. Connections are tight at air bridge and MAF sensor. Stalling is less if the A/C is not on, but when you switch it on, the idle will hunt down to below 500 rpm, and/or stall.
It did not do this in the past, and the only change I can think of is a dealer GM reflash in connection with the MN6 recall. That, and the mileage. I've also tried Techron.
Oh, yes, it also seems to be running a lot more "boggy" at the low end in the higher gears (4th and up), until about 3,000 rpm plus.
Thanks for any help, suggestions.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
How did you clean the MAF??? Your maf could be bad or reacting funny to the descreening. With out any codes and lack of tuning software or a TECH II, it's difficult to figure out whats going on. Have you ever cleaned the throttle blade??
The part that bothers me is that the AC "ON" input causes that much problem. Are you SURE that you have a completly sealed system between the MAF and the throttle body?? How about other vacuum related leaks? Here are some areas that are common air leak areas on a LS1, LS5:
PCV rubber hoses and fittings dry rot and crack.
Intake manifold not seated properly DIRT between the seals or LOOSE manifold bolts.
Brake booster vacuum line loose or cracked.
HVAC vacuum line on the back of the maniforl leak.
MAP sensor leak
Bad MAP sensor!
PHIL,,,,,What is RAF??
Bill C
The part that bothers me is that the AC "ON" input causes that much problem. Are you SURE that you have a completly sealed system between the MAF and the throttle body?? How about other vacuum related leaks? Here are some areas that are common air leak areas on a LS1, LS5:
PCV rubber hoses and fittings dry rot and crack.
Intake manifold not seated properly DIRT between the seals or LOOSE manifold bolts.
Brake booster vacuum line loose or cracked.
HVAC vacuum line on the back of the maniforl leak.
MAP sensor leak
Bad MAP sensor!
PHIL,,,,,What is RAF??
Bill C
Last edited by Bill Curlee; Jul 19, 2006 at 02:18 PM.
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Thread Starter
Race Director
Joined: May 2000
Posts: 14,542
Likes: 5
Originally Posted by willyfastz
Did it start acting up right after the reflash? If so do you know if the car had been tuned before. And make sure you didn't hurt the maf wires when cleaning them.
FWIW -- the idle problem statred before the first cleaning of the MAF wires. That did nothing to solve it.
Thread Starter
Race Director
Joined: May 2000
Posts: 14,542
Likes: 5
Originally Posted by Bill Curlee
How did you clean the MAF??? Your maf could be bad or reacting funny to the descreening.... The part that bothers me is that the AC "ON" input causes that much problem. Are you SURE that you have a completly sealed system between the MAF and the throttle body?? How about other vacuum related leaks?
All my reserach points to a vacumn leak or dirty TB. A friend of mine and I will quadruple check the connections and clean the TB this weekend.
Keep you all posted.
Thanks for the responses.!
Safety Car
Joined: Sep 2000
Posts: 3,604
Likes: 395
From: Austin, TX
I just went through hell with my car surging, idling like crap etc. Doesn't sound like your symptoms are the same but I figured I'd mention this any just in case it helps.
After spending more money than I needed to it ended up being a broken wire inside the IAT connector plug.
After spending more money than I needed to it ended up being a broken wire inside the IAT connector plug.
Thread Starter
Race Director
Joined: May 2000
Posts: 14,542
Likes: 5
Found the problem, and thanks to NYChasm for the help (we fixed it in his driveway).
Turned out to be a vacumn leak between the end of the MAF sensor and the air bridge.
There's an indexing tab on the bottom of the stock air bridge that mates with a notch on the rubber seal, and when the Chevy dealer mechanic installed the air bridge the last time, he neglected to locate the notch with the tab. Once we aligned those two pieces, everyhting ran OK.
For reference, if you have the Donaldson assembly, it's probably best to assemble the entire filter to throttle body sections outside the car, check all the conncetions, and then put it in the car as one unit.
The mechanic hadn't done that, hence the problem.
Thanks again to everyone for the input. 
Turned out to be a vacumn leak between the end of the MAF sensor and the air bridge.
There's an indexing tab on the bottom of the stock air bridge that mates with a notch on the rubber seal, and when the Chevy dealer mechanic installed the air bridge the last time, he neglected to locate the notch with the tab. Once we aligned those two pieces, everyhting ran OK.
For reference, if you have the Donaldson assembly, it's probably best to assemble the entire filter to throttle body sections outside the car, check all the conncetions, and then put it in the car as one unit.
The mechanic hadn't done that, hence the problem.
Thanks again to everyone for the input.
