THSCC Forums

At idle, the car will go from about 50 to 1000 rpms for several minutes. While driving using the gas pedal very lightly, it wants to cut out on me.

I talked to steve who had similar issues with his car and he recommended me to get some fuel injection cleaner. My concern with those types of products is, what else is it doing other than cleaning the fuel injectors?

So, does anyone know about these chemicals and what they do? The fuel filter only has like 20k on it, the car has about 180,000k.

phil

I've used 2 fuel injection cleaners with good success. For everyday maintenance, I use a bottle of Chevron Techron just before every oil change. I've done a fair amount of research on fuel injector cleaners, and Chevron gets almost universally good reviews. It's not terribly strong, so you may have to run a couple tanks with it. Any autoparts store should have it.

Not a chemist here, but what I've read says that during combustion some of the stuff in Techron can slip by the rings and get into the oil - this is why you want to use it before the oil change. I've also read that you can use it up to 5 times during a single oil change without the oil deteriorating too much. YMMV

The other product is BG 44K. In theory, it's very similar to Techron - a fuel injector / combuston chamber cleaner. It's a lot more concentrated, however. It's also a bit harder to find. You might need to make a trip to a CarQuest for that one.

If that doesn't work, you may want to look at a top-end engine cleaner like the one GM dealers sell. It's pretty harsh stuff, but with a 180K motor, it might be worth investigating.

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Tom Freeman
'98 M3/4/5 | '93 Spec3 325i | '12 TSX sport wagon | '03 Tahoe
Team Silver Bullets '91 240SX

Phil,
I could be in left field here, but I've usually found idle surges to be solved by finding a vacuum/intake air leak. The "hunting" is caused by the ECU trying to compensate for air getting into the system that the air flow sensor doesn't "know" about (the leak).

Frank

Oh, what Frank said...

I've seen this on a couple of Mitsubishi's - Jason Mauldin's Mirage and Ryan Holton's Talon. On those Mitsu's, there's an Idle control screw assembly. As they age, the seals become hard, and air sneaks by, leaving the ECU to pulse the idle while it tries to figure out where the extra air is coming from.

On Jason's car, the screw was still there with air leaking by. On Ryan's car, the screw was gone entirely.

So...it could very well be some kind of vacuum leak. I'd imagine you still have plenty of original vacuum hoses, and one of them could very well have a small hole in it.

A step to diagnose this it to spray a little carb cleaner near a potential leak. If engine speed increases audibly during the spray, you've found a leak.

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Tom Freeman
'98 M3/4/5 | '93 Spec3 325i | '12 TSX sport wagon | '03 Tahoe
Team Silver Bullets '91 240SX

All of the replies so far are on the right track. Another thing to check is the mass air flow sensor. If the sensor is dirty or you have a K&N Air filter in there and have over oiled it, the oil will collect on the sensor internal wires and cause funky idle. I had that happen to my BMW, Miata, and Celica. Easiest way to clean it is pull the sensor and spray the inside with brake cleaner. - AB

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'14 Toyota Sequoia Platinum 4WD
Super Westerfield Bros - '93 Integra - LeChump Du Jour
STX 93 - Scion FR-S

Tom,

So I bet you wouldn't be surprised to know I own a '91 Plymouth Laser with the Mitsu 2.0L motor? My intro to idle surging ....

Frank

Don't know if this applies to your first-gen CRX, but my second-gen has also had idle surge problems. Besides what's mentioned above, CRX's are supposedly known to be sensitive to air bubbles in the coolant affecting the water temp sensor and throwing the ECU off. I bled the (small amount of) air out of my system and haven't noticed the surging since. But YMMV.

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Dustin Fredrickson
-- I'm a nobody --