CKit

So there are a quite a few threads about this topic:

SYMPTOMS: Car bucks, sputters, sometimes when you give it gas it hesitates, bogs, then lurches forwards. Sometimes it doesn't run clean to redline and stumbles a little. Not smooth.

OTHER ASSOCIATED SYMPTOMS: If you rev to redline, it feels like it "clears" the engine temporarily. Usually no CEL despite the rough driving.

FIRST EXCLUDE: That your shifting / clutching needs work. This shouldn't be the cause if you're in gear... pushing the gas... and you're getting the lurching. Also exclude frank heat soak. If you're idling in 100 degree traffic and bog off the line, that's something completely different.

YOU'VE TRIED: Checking the plugs, MAP whack, fuel injector cleaner to the gasoline. Only temporarily solves the problem if at all.

This happened to me in 2004 when I was stock. I'd have to pull the ECU fuse to reset it and it was frustrating to drive around town. I checked all of the above and nothing really helped. I went to the local lube place and had them do the 3-step injection cleaner: spraying the throttle body, gas additive, and something else.

That solved the problem completely.

In 2007, I noticed some of the stumbling again. I chalked it up to a helicoil in the #2 cylinder head from when a loose spark plug ripped out a few threads in the head. So I was constantly tweaking the Comptech FPR and would run super rich to compensate. My tail pipes were black and I went through plugs quickly.

Last month, I had the head replaced. The stumbling remained. Saw this thread in UTH: https://www.s2ki.com/forums/index.ph...ic=478799&st=0

Felt bad for the guy who has replaced a bunch of parts with no relief.

Thought this picture made a lot of sense:

(Thanks, db17k)

I always doubted the veracity of the "MAP whack" theory. Those connections are pretty snug and I had a hard time believing that a loose connection was responsible for all the "MAP whack" problems.

But look at the picture: Air delivery down to the MAP sensor has to travel down that little slit in the throttle body. All it would take was a little bit of dust / grime / oil to build up and narrow / clog that passageway. And what's worse, if the flow of air was disrupted and not laminar, you could get inconsistent readings.

It made sense that a MAP-like problem could persist despite jiggling, whacking, cleaning, and replacing the MAP sensor itself... if the passageway was clogged.

Soooooo.

I cleaned it and my car runs perfectly now. No stuttering, stumbling. It feels "clean" and not "muddy" anymore. I think that in 2004 when they were spraying the cleaner right at the throttle body plate, they inadvertently cleaned the passage as well.

I personally cleaned it in the following way (because I'm lazy).
1. Unclip the MAP sensor
2. Unscrew the MAP sensor (two Phillips head screws, that's all)
3. Use light sprays of alcohol or compressed air to clean the inside of the MAP sensor.
4. There is a silver "well" in the throttle body that the MAP sensor sits in. If you look carefully there is a tiny hole in the side of the well towards the firewall. If you have a tiny wire or pipe cleaner you can roto-rooter this first. Then pour very small amounts of alcohol into the well and use a squeeze bulb or physically blow on the well to clean the passage. There was resistance when I first tried blowing... I repeated this three times. The small amount of alcohol (about 10 drops per time) shouldn't cause a problem when starting the car later.

I can take pictures if anybody still has questions.

Post up if this helps.

NOTE: this will NOT help if you have another significant problem, like an untuned VAFC or fubar'd spark plugs. This is for the people who have looked and looked, but the car still stumbles intermittently... kind of like the MAP whack symptoms, but it doesn't improve even after swapping MAPs.

db17k

thanks buddy!

Butch777

Wow, Sounds exactly like the same problem I had with another car. A buddy of mine sprayed brake cleaner in and around the fuel system and then it worked great. I'll have to remember this. Thanks, Butch

__redruM

Makes sense, back in the 90s when I worked as a mechance we sold a service called a throttle body service. Basically we cleaned the throttle body out with carb cleaner and a rag. This usually took care of an assortment of idling and perfomance issues. They certainly gunk up overtime. Especially if you're running rich.

Good find.

JS2k.com

Thanks! Will try it soon. I will bog sometimes.

CKit

This could also explain why the "MAP whack" worked for some people temporarily... you could tap on the MAP sensor and knock some of the crap out of the throttle body... which would only help a little for a short period of time.

Went driving today. The car is fantastic. "Crisp" is about the best way I can explain how it feels.

Avernus

Nice work!

toofast4yalll

Nice! Never would've thought to try that.

CKit

Instead of alcohol, was thinking about carb cleaner, but didn't want too much to be sucked into intake.

TheDonEffect

Good stuff, finally an answer to an age old question.