98 Suburban has intermittent stutter

[IFallsRon]

Every few days I get a low-RPM stutter-like miss. I doesn't seem to show as I speed up. New plugs and wires this summer. I've added a couple bottles of iso and some injector cleaner and twisted all the wires. Any guesses before it goes to the garage?

[Jeremy airjer W]

So it runs ruff at idle?

I can tell you that there is no need to use ISO in your fuel tank unless you drive through an auto car wash with the fuel door open and the gas cap off. There is plenty of ethanol in the gas that will absorb any condensation that may occur in the tank. Also every time you add a bottle of ISO you are essentially raising the octane rating of the fuel, which can potentially lead to decreased fuel economy and performance.

Anybody else have an opinion on using heat(isopropyl)?

[Scott K]

Yes, like you said, dont do it, unless you know you have water in the system.

[fish2live]

sounds like it could be a dirty maf sensor.

[IFallsRon]

Not so rough at idle but noticable at enough RPMs to move and it's not every day.

[Jeremy airjer W]

What about the cap and rotor? I'm guessing there is no check engine light as well.

[IFallsRon]

It ran rough on and off all week and I got the Check Engine light on Friday and stopped at a parts store to get a scan. It was something related to ignition but too general to pinpoint anything. The engine smoothed (and the Check Engine light went out) before I left the parts store parking lot and there's been no stumble since.

[Jeremy airjer W]

P0300 maybe?

[Shack]

I would guess random cylinder misfire also!

[deadeye]

The ignition control module was a problem sometimes on those trucks. They can give you low speed issues and work fine higher up in the rpm range.

The cap and rotor on that one is also a weak point, but it would not likely be an intermittent problem.

[sparkydm]

Not sure if this helps at all, I had trouble with my chevy van stumbling and dying intermittently. I noticed that the temp gauge dropped out each time it happened. So then I knew there was a short somewhere. Found it in the harness where it was resting on the upper control arm.

[IFallsRon]

I pulled the distributor cap this morning and all the contacts had a green Rip Van Winkle beard. I've never seen a cap with that much stuff. That cap was new within the past six months and I'd like to thank the local NAPA store for replacing it for nothing.

I'm guessing there's some kind of moisture problem. I used to have a problem with the 88 Silverado where I'd get some leakage from the manifold water neck and it would wick back to the cap and cause problems but I fixed that with a new hose and clamp.