Engine Idle Fluctuates Approx. 150 RPMs

[Howard H]

After my '74 2.0 has been idling for a couple of minutes, the idle begins vacillating from about 950 to 1100 RPM.

A friend who noticed it suggested to me that it might be a worn distributor, which keeps changing the timing.

I know just enough about the ignition system to be dangerous, so I am putting the question out there --- does this seem feasible?

If so, would a Crane XR700 (or similar ignition system)cure this problem? If not, what other possible causes of the problem should I look for?

I appreciate all responses. (Thanks again to all who have been so willing to share their knowledge and experiences in the past.)

Howard Henneman

[jmcleod]

my guess is (just a guess) that an electronic ignition won't cure a worn distributor (unless you get a crankfire system).

[Dave at Pelican Parts]

Sounds like a "lean hunt" to me. Try richening the idle mixture a couple of "clicks". Turn the knob on the ECU clockwise. Count the number of clicks so you can get back to where you started.

Chances are the hunt will either go away, or at least not be quite so bad.

--DD

[Germain]

I'm not questioning your abilities with a car, but I have to ask.

Did the engine tone change, or just the tach?

If just the tach its noise on the line.

[bowlsby]

It does sound like its running lean to me, or maybe a small intake vacuum leak, but that another story.

My 74 2.0 was recently running worse than yours, vascillating about 500 rpms and even died once until....

I took it to a local respected 914 P-car mechanic. He used an exhaust gas analyser and fiddled with the pressure sensor. Dialed the mixture up to about 4.5% CO level...he says thats the level these engines like. The car purrs like a kitten on 87 octane. This is a slightly higher CO level than the smog dr's like, but he told me that I could lean it out enough for my next (and hopefully final) smog cert, just with the ECU control...count the clicks.

He also told me that the factory, for smog control reasons, has intentionally set the pressure sensors to run too lean for these engines. This lean condition makes the engines run hotter, reducing their longevity...but satisfies Sacramento.

I'd take it to a good shop and have them calibrate it...best money I've spent on the car ever.

[Howard H]

No offense taken to my abilities (or lack thereof). The fluctuation in rpm is very audible at that engine speed range. The pitch varies in sync with the tach movement.

I'm going to check for an intake vacuum leak first. If I can't find the leak, I'll make the ECU adjustment. (May make the adjustment even if I do find the leak.)

Following up on the intake leak --- Is it best to spray carb cleaner or starting fluid around all the intake connections?

Howard

[JP Noonan]

Starting fluid is WAY too flameable to be used this way!!!! Carb cleaner is much, much safer.

[Howard H]

JP, thanks for the safety tip. I'll use carb cleaner for the test.

Will advise all as soon as I find and correct the problem.

Thanks for the responses.

Howard