b-townrally

Hello everyone, Im trying to fix my rough idle on an 86 audi 4000cs. Ive made a little harness to hook up to the control pressure actuator. At warm idle it reads between 19.56 and 19.57mA. My temp senders are new and read around 350ohm warm. My O2 sensor is new and reads cycles in a range between 200 and 700 millivolts.

To the best of my knowledge ive fixed all major vac leaks, ive replaced all of the vac lines in the engine bay except for the formed rubber parts on top of the cam cover.

I adjust the set screw in between the rubber boot and fuel distributor but the mA dont change either way. I'm following the write up on Huw's audi garage to test all of this. BTW, I havent clamped off the line off of the cam cover like it recommends because i cant figure out how he did it, would this make a big difference? Any ideas on what I could try next?

Thanks everyone for listening to my rambles...

b-townrally

anyone have any suggestions?

westco4K

not trying to dumb it down or anything, but has the air flow meter under the big boot been cleaned?? they can get sticky, dirty and overlooked quite often

b-townrally

hey any help is appreciated. I have cleaned it up a bit, i put in a new air filter and the plate moves up and down with a small amount of resistance. Is there anyway the CPA could be bad?

UPDATE: I was tinkering with it more today. When I had the harness hooked up to the CPA, I started it when the motor was pretty warm, the meter read around 9 to 11 mV. This was while it was running like total crap on anywhere from 2 to 5 cylinders. Once I revved it up past 2k to make a cylinders fire it jumped up to 20ish and then dropped back to 19.5mV at idle.

I dont what it means but it might mean something

b-townrally

Sorry I meant mA not mV

westco4K

that drop in amperage seems odd but I can't say I know what the operating range is so it's hard to say if thats the problem. does it run poorly all around? or is it just an idle issue? what condition are the ignition components in? how about other key players like the injectors themselves? I had an 85 jetta gli that would run great one day and horrid the next. I kept assuming it was a CIS issue and chased that for weeks on end, swapping fuel distributors, control pressure actuators, injectors (one was leaking but still not the problem), played with timing. . . . ended up bieng the knock sensor wiring, one day I had good connection, the next i didn't and it was pulling the timing back so far it would barely run.

I don't think this is your problem, but that car tought me a valuble lesson, (which is why I bring it up alot) look at the entire picture before zeroing in on one component. sometimes the problem is the last place you would think to look.

also, one more recent story. swapped out engines on a buddys mk3 jetta. ran poorly under load, could not figure it out till we were trouble shooting one evening in the dark and noticed one plug wire was arcing against the block. they never had an issue on the old engine but it was one of the few parts that didn't get replaced during the swap. changed them out and it runs great now. I was hung up on the MAF sensor and it turned out to be one simple plug wire. lol

b-townrally

It runs quite well over 1500 rpm. All ignition components are new such as; cap and rotor, plugs and wires and coil. All injectors are new and I flow tested them before i put them in. It has new fuel filters and pump and lines.

It runs real rough on initial start up, only runs on 2 cylinders or so. Once it gets warmed up it runs around 1000 rpm on all cylinders but it smells rich. Plugs have a fair amount of carbon build up when I take them out but nothing to extreme. Cleaning the plugs makes no difference.

Im going to check timing to be sure and see if that does anything

b-townrally

Update: when I unplug the temp sender for the ECU it idles better but a little higher, even when it was cold. I tested the temp sender and the resistance was within spec.

b-townrally

also found a nice vac leak around the boot where it attaches to the throttle body. Any tips on how to seal that up?

Rogviler

Permatex black works really well. Just be sure to clean the boot and then clean it again.

I would also do a proper vacuum leak test, using a cigarette or cigar (or borrow a friend who smokes), and blow smoke into a vacuum line. Makes it dead easy to see any leaks. Just a 1/4" hole can make the car not even run, so you can imagine what can happen with little tears and cracks.

-Rog