Subject: Re: rv8flyboy, any luck on your idle issue? Author: rv8flyboy : member since September, 2007 : 2970 posts Posted on: 2011-09-23 10:05:41

you may be spot on!!

I for sure found that I had a bad sparkplug wire connection at the distributor cap. This irks me somewhat as A: the set was new and B: I was the one who made the set

Of course it was for the # 12 that holds the CylId sensor. The main clue for me was when I put an oscilloscope on it and found that my injectors were not firing alternating, at random. normally they fire in groups of 3, but lose the CylId sensor and now all injectors fire at the same time. that appears to upset the mixture control.

after I fixed this I started chasing my own tail. Because the car ran rich, the O2 was carbon'd up. This made the response time very slow, which caused the DME to hunt for the correct mixture, which showed up as a bad O2 suspect, which caused the car to run rich, which caused the O2 to carbon up ...... and I was still looking for a problem


The light bulb finally went on and I decided to take the car on a good highway run and do a throttle sync (been disconnecting them DME's). My car smoked like it was on a diet of SeaFoam and water for about 5 miles, then things settled down, the idle turned back to normal.

my mileage is still a bit higher than I like it to be but the way to work has gotten busier and there is considerably more stop n go traffic.

I had harvested several ignition wire sets over the years as spares. When this started, I measured all of them. Out of the 4 sets ( 2 left and 2 right) NON was complete. All had at least one lead that was open or way off on resistance. The sparkplug connector should be 5 - 6K and the distr connector should be 1Kohm.


as a data point, un-sync'd DK's also give very poor idle AND run up the fuel consumption. I learned that the hard way when I disconnected my battery last year for only 10 minutes. Afterwards my car idled like an old diesel tractor, but being in denial, i did not believe that 10 minutes would do anything.... I was very wrong on that.

a quick sync and all was well, took me 2 weeks to come to that conclusion, nobody argued I am fast on the uptake

750IL 1990 (9/89) Black, 90K,


also currently stabled:
540 w. 6sp, 1995, Black

I told my wife, it is not a Boy Toy, is a Man's Machine!!

• rv8flyboy, any luck on your idle issue? - Rich 1990 750iL 2011-09-23 07:21:38 (136 views)
  • Re: rv8flyboy, any luck on your idle issue? - rv8flyboy 2011-09-23 10:05:41 (152 views)