ivangene

so this is getting worse (in fact the video is the worst its ever done)

ssems smooth at idle, if I just "touch" the trottle it does this....ussually recovers quicker than the vid. if I drive it it doesnt do it.....

lets take one step at a time, I have a couple other issues to take care of next....

anyhow, I was thinking CHT sensor or a dirty/bad idle speed adjuster valve (thing)

TIA

windsoreight

Mine does the same thing. Yours sounds like it idles higher than mine. Mine idles around 700 rpms and surges up and down about 100 rpms.

User 4221

This has been well covered on Pelican. But as a starter, this is usually caused by a vac leak or improper mixture.

Mine was bouncing between 800 and 1200 on cold start. This lasted about 30 seconds to a minute.

I adjusted the mixture and it fixed the problem.

HTH,
Scott

theiceman

i think hunting is rich . I owuld start having the baseline CO measured and adjusted .. can you get your hands on an LM1 ?

User 4221

Mine was actually lean and I had to richen it up.

I used the poor-boy method of measuring voltage on the O2 sensor and dialing it in this way.

Mine would also stumble when pulling the oil cap loose as noted on PP. It wouldn't die but would idle really rough.

I may need to replace the O2 sensor sometime but it is running strong for now.

ivangene

I do hear vaccum but thought a leak would cause more of a rough idle all the time. - guess I have some learning to do. BTW LMI - hmm, dont have one of those
and then to find the mixture but I am betting its a vacuum leak soI will need to start there before turning screws...method = propane torch (unlit)?

theiceman

That seams to be the common aproach .. but even if you can borrow an LM1 it eould be a good starting point.

rusnak

I think Iceman is 100% on the money. If you can get an LM-1 with a wideband O2 sensor, then you'll quickly be able to see what is going on. A lot of times, an old or faulty O2 sensor can cause the dme to run rich, even in closed loop.

Scott, yours sounds like it's running lean for some reason, or perhaps the O2 is old, as you suggest.

About a year ago when Russell Berry was on the board, he suggested an open loop AFR of 14.2 lambda as a baseline setting. I tried that, and lo and behold, it was perfect. Basically you disconnect the DME O2 sensor, and connect the test sensor in it's place. Adjust the air bypass screw in the AFM. I think .08 CO or so is the stock setting if you are using a CO meter, which you can rent at a good auto parts store.

What I ended up doing was install a cat bypass with two O2 bungs, one for the DME and the other for the tester. Then I drove the car in different situations, and I could see the O2 sensor react under load, and at WOT. It's a great excercise, and if you have a vacuum leak, you'll see the highway mixture actually lean out at high rpms before the system compensates.

Vacuum leaks will cause idle bounce, especially at high ambient temperature with the engine hot.

rusnak

Ivan, do you have a Bentley manual? You should go through the resistance checks and check the idle position switch as outlined in the test regime in the section covering fuel injection and engine management. Was the engine warmed up, or cold in the video?

ivangene

no bentley - its a hard book right?
will search and order this W.E.

the technical jargon in the above post is very intimidating to me - I will have some learning to do I see.

theiceman

Ed it's pretty easy actually once tou get into it .
The Bentley is a soft cover and worth it's weight in gold ..

I will post a pic of my LM1 output so you can see what we are talking about ..

User 4221

I'm definitely lean. I've got the mixture screw maxed out and an O2 sensor voltage of 0.65V. I'm on the edge.

Either the sensor is shot or I've got vacuum leaks (which I suspect both may be the case)

Carlo_Carrera

My car did the same thing. I brought it to good a shop and all they did was recalibrate the CO using a probe in the tail pipe. It took less that a hour and only cost me $90. It was the best $90 I ever spent.

Get your CO checked.

theiceman

i think there is a hidden message here somewhere ..

rusnak

actually I mis-typed earlier. 14.2 afr might be around .95 or maybe .97 lambda or something like that. I'd have to go look through old files to be sure.


Ivan...the Bentley Publishing manual sometimes shows up on Amazon or Ebay. It's worth it, and very easy reading. There are some air fuel threads, as well as a good one by Draco on testing the AFM (air flow meter) with a 9 volt battery.