5.7 v8 rough idle, hesitation and shudders in reverse and drive only

[98sub1500]

First off, I drive a 1998 GMC Suburban K1500 SLE with the 5.7 V8.

Not too long ago I had the rear drums checked, front brakes replaced and a brake fluid flush. Since then, never before, for some reason I have the occasional shudder/hesitation while on the accelerator and a rough idle ONLY in drive and reverse while not moving. The truck idles and revs smoothly in P and N. Its happened on the highway 70-75mph, on backroads at 35-55 and while not moving. Using 3 2 1 instead of drive makes no difference, issue is still present. There seems to be no rhyme or reason to it happening however I went through a car wash today and as soon as the water jets hit the underside it triggered that shudder/hesitation. Usually I shut the truck off and let it rest for 10-15 min which seems to take care of the issue until it happens next.

The truck has thrown one code, a P0102. I noticed the air intake tube was not seated in the filter box properly and fixed that. I have also installed new spark plugs. This truck is new to me.

I haven’t dove too deep into it yet because i’m still very confused. Any thoughts and suggestions would be very much appreciated.

 

[ralmo94]

I usually start with a good thorough visual inspection of all vacuum lines and connectors.

p0102 is Mass airflow sensor low, could be signal dropping off from it.

Is there an oiled air filter?

common issue is over oiling them and the oil contaminants the MAF.

you can get a can of mass airflow sensor cleaner and clean the sensor, if it's not the problem, at least it will be clean.

 

[Schurkey]

The above, plus connect a scan tool, look at the data while the engine is running rough.

Misfire counts in particular. That would at least tell you which cylinders have problems.

 

[GoToGuy]

O2 sensors wiring? The water blasting under body?

 

[Schurkey]

1998 GMC Suburban K1500 SLE with the 5.7 V8.

I have the occasional shudder/hesitation... ...I went through a car wash today and as soon as the water jets hit the underside it triggered that shudder/hesitation. Usually I shut the truck off and let it rest for 10-15 min which seems to take care of the issue until it happens next.

O2 sensors wiring? The water blasting under body?

Maybe. Seems somewhat unlikely.

1. If the O2 sensors were shorted-out by water, I'd expect to have one or more codes set.
2. O2 sensor wiring is fairly well-sealed against water.
3. It's hard to say that this happens as soon as the car-wash underbody jets start up. It could just as easily be the top-mounted water jets, and it takes a few seconds for the water to drip on the ignition coil or distributor from a leak at the back of the hood, for example.

Any of this might dry-out in the ten or fifteen minutes allowed "rest time". It could also be total coincidence--he gets misfire at highway speed, too.

Along with the other suggestions from earlier posts, I'd be checking for proper spark with a spark-tester calibrated for HEI, at the plug end of the plug wires, while misting the coil and cap with a spray-bottle of water. Given the Vortec distributor cap, I'd be checking #3 first of all. #3 seems to be the troublemaker on Vortec caps.

 

[98sub1500]

Maybe. Seems somewhat unlikely.

1. If the O2 sensors were shorted-out by water, I'd expect to have one or more codes set.
2. O2 sensor wiring is fairly well-sealed against water.
3. It's hard to say that this happens as soon as the car-wash underbody jets start up. It could just as easily be the top-mounted water jets, and it takes a few seconds for the water to drip on the ignition coil or distributor from a leak at the back of the hood, for example.

Any of this might dry-out in the ten or fifteen minutes allowed "rest time". It could also be total coincidence--he gets misfire at highway speed, too.

Along with the other suggestions from earlier posts, I'd be checking for proper spark with a spark-tester calibrated for HEI, at the plug end of the plug wires, while misting the coil and cap with a spray-bottle of water. Given the Vortec distributor cap, I'd be checking #3 first of all. #3 seems to be the troublemaker on Vortec caps.

I noticed some parts of the intake weren’t seated properly. I got it all put back correctly and also cleaned the MAF sensor. Since I’ve put on well over 1,000 miles of highway/backroads driving and haven’t noticed an issue at all. I wonder if the spray of the water knocked some components loose and caused a large vacuum leak. Regardless, I think my issue is solved. Thanks for the replies.