Occasional Sputtering

[trevcda]

New topic? Probably not. But here goes.

98 GMC Safari, AWD. When I gently accelerate, at the point when it's about to shift, it sputters and feels like it's missing. It also does this when cruising around 70mph. I can put my foot into it and it will push through, but at that point where your just keeping it at speed, it sputters occasionally and feels like it's getting worse.

So far I've replaced plugs, wires, cap, rotor, new K&M air filter, fixed a vacuum leak, new fuel pump and fuel filter and ran some gas additive to clean fuel system.

I was getting ready to take it in for injector cleaning, but I'd thought I'd running by here for some opinions.

So what do you guys think? You guys have helped me with other issues, directly and indirectly so thanks for any advice.

[Smiliesafari]

Have you cleaned your Mass Airflow Sensor? The oil from your K&N air filter can cause problems.

[trevcda]

The filter is new enough that I wouldn't expect that to be the cause. Having said that I have never cleaned my mass airflow sensor. I'm not even sure what it is, where it is or how to clean it! I do know that what ever it is, I have never cleaned it! Would they have touched when I had it tuned up recently with plugs, etc.?

[MountainManJoe]

It's just downstream of your air box, behind the honeycomb screen. Looks like this...

Very carefully clean the three thin pieces of wire with an aerosol cleaner. They are sensitive to deposits.

[Macecyn]

These are the exact symptoms my '99 LT has. Just performed the suggested work and will test it this afternoon. The wires were immaculate but I did it anyway....

[Macecyn]

These are the exact symptoms my '99 LT has. Just performed the suggested work and will test it this afternoon. The wires were immaculate but I did it anyway....

Ok, no luck on this quick fix. Here is a little more detail.
I liven Dallas, and not many hills around here, but about 100mi west of here on I-20 is a hill that is about 1/2 mile incline. EVERY time I get about 3/4 up, it starts to sputter, Loss of power, often times the check engin light come on, blinks, goes off after 20-30 miles. My mechanic can find anything wrong and resets the codes.

[LiftedAWDAstro]

It would help if we knew the codes. Might be a heat issue with the ignition coil or module.

[trevcda]

One of my codes is P0108. I think that was a MAP sensor or something.

[MountainManJoe]

http://www.obd-codes.com/p0108

[Macecyn]

Thanks for this info. Interseting because I am definately having vacuum issues, even afer having replaced the lines and installing a larger vacuum "ball" or whatever the technical term is (When I accelerate hard now air is routed thru the defrost outlets, and it reverts to the a/c vents when lettiing up on the gas).

[MountainManJoe]

your vacuum valve could be shot too.
viewtopic.php?f=55&t=746&p=85054#p85054

[Macecyn]

This is good stuff! Thanks timeless.

[trevcda]

Now here's something interesting. I accidentally put in supreme unleaded as opposed to the regular unleaded gas that I usually use and haven't noticed the sputtering I mentioned in my original post. It's been running really smooth. I drive a hundred and some odd miles round trip to work everyday. I'll see how this pans out tomorrow morning, as that's usually when it's at it's roughest, and report back.

So what would this indicate on my Safari, given the above information? I had a 99 Buick Riviera that deplored anything but supreme and would run rough anytime I tried to feed it anything else, but the owner's manual actually said as much, so it wasn't too much of a surprise. I think that had something to do with the supercharger on that engine.

[MountainManJoe]

The VCM uses the MAP sensor to control fuel delivery and ignition timing, so your incorrect MAP readings are probably causing the engine to knock. High octane gas resists knock.

[trevcda]

Still a few misses but nowhere near what it was on regular. One new MAP sensor, coming up! Is there a tutorial around on changing this out? It's probably dead simple, but I'd rather know what I'm getting into ahead of time.