Idle Speed Motor Question - Rough Idle and Hesitation on Acceleration

[DeLorean937]

Im currently trying to diagnose my idle speed and roughness on acceleration. When I accelerate the car is pops and sputters and has no power. The only way I get it to speed is to nurse the throttle up above 2000 RPM then it takes off fine. I checked timing and got the mixture set to get the car started and running and not die when I place it into gear. I seem to get things adjusted perfect then sometimes in goes back to ruff driving. I took things apart to check around. I found the CSV brass pipe was moving around and leaking so I got it secured down.

I'm checking my idle speed motor at the moment. I have it in my hand connected, engine is cold, when I depress the micro switch the rotor inside moves only about a quarter of the way? Is it suppose to open all the way or only when hot?

[DeLorean937]

Forgot to mention that I tested the ISM but powering the center pin and grounding each side and valve open and shuts to the max without issue.

[Bitsyncmaster]

If you adjusted the mixture to get the best idle, your mixture is probably way rich. You really need a meter to adjust the mixture correctly.

[DeLorean937]

If you adjusted the mixture to get the best idle, your mixture is probably way rich. You really need a meter to adjust the mixture correctly.

I adjusted the mixture to get best performance on acceleration. Idle was high but I lowered it using the lower arm screw and micro switch screw still hesitates on acceleration of i can get into gear without dying.

[Bitsyncmaster]

I adjusted the mixture to get best performance on acceleration. Idle was high but I lowered it using the lower arm screw and micro switch screw still hesitates on acceleration of i can get into gear without dying.

A lot of things can cause your problem. For it to be missing at low RPM it could be ignition but that usually has problems more so with higher RPM. I'm just guessing your to rich and fouling the plugs or the rich mixture is causing pre-ignition.

[Michael]

I can guarantee you your mixture is off, probably way off. You can not adjust the mixture by sound, you can barely get it ballpark close (which is a nice way of saying it's way off). Some say you can get it close by unhooking the o2 sensor and going clockwise until the engine stumbles. 1/8 of a turn makes all the difference in the world, there is no close.

You need a 20 dollar meter and only after you have confirmed all vacuum leaks and linkage settings are correct as well as dist. advance and confirm the idle circuit is working properly and the stops are adjusted correctly. There is a lot to check there. Mixture is usually the very last thing to adjust.

Over the years of P.O.'s many mixtures were tampered with to compensate for something else, then adjusted again to correct yet other problems.

[David T]

The common causes are a bad CPR, vacuum leaks, dirty injectors, fouled O2 sensor and now that you messed with the mixture adjustment, the mixture is way off. You probably need a tune-up too. Before you can even attempt to adjust the mixture you need to make sure all of the secondary ignition components are good and you have NO vacuum leaks. Depending on the mileage you may also need a valve adjustment. You cannot adjust your way out of these problems, they have to be fixed and THEN you might have to make a minor adjustment. The mixture screw is VERY sensitive, a 1/16 turn is a lot. In most cases you are better off not touching it, it is closer to where it needs to be than you will be able to set it (assuming no one got to it yet!).

[dn010]

Make sure the 3 brass air screws are fully seated too, the PO of my car had these all open back when I ran the stock engine and it caused all kinds of problems!

[mluder]

Make sure the 3 brass air screws are fully seated too, the PO of my car had these all open back when I ran the stock engine and it caused all kinds of problems!

And sometimes opening them slightly can SOLVE all sorts of problems.

Cheers
Steven

[DeLorean937]

And sometimes opening them slightly can SOLVE all sorts of problems.

Cheers
Steven

It helped a little bit by lightly seating them. But I was wondering if the micro switch is depressed when cold, is the idle speed motor suppose to open all the way?

[Bitsyncmaster]

It helped a little bit by lightly seating them. But I was wondering if the micro switch is depressed when cold, is the idle speed motor suppose to open all the way?

I think it should close all the way when the engine is not running. I run my own idle ECU now but that is what I remember with the stock ECU.

Normally the idle motor starts about half open but it's position does depend on the engine temp.

[DeLorean937]

ISM seems like its buzzing with the microswitch pressed and the flap is closed. When I depress the microswitch it opens about a 1/4 of the way. I got a dwell meter and hooked it up when running the car I connected the lead of the orange wire and the other to ground. The needle does sway like ive seen in videos but rather just stays pointed at 60. Makes no difference when I adjust the mixture. 02 senser is hooked up and FV is buzzing.

I read a post where a ISM can short out the Lamba ECU so I was wondering if it might have. I metered the center pin of the ISM harness and am getting 11.26V at the pin and only 3.38V on the right pin.

[Michael]

ISM seems like its buzzing with the microswitch pressed and the flap is closed. When I depress the microswitch it opens about a 1/4 of the way. I got a dwell meter and hooked it up when running the car I connected the lead of the orange wire and the other to ground. The needle does sway like ive seen in videos but rather just stays pointed at 60. Makes no difference when I adjust the mixture. 02 senser is hooked up and FV is buzzing.

I read a post where a ISM can short out the Lamba ECU so I was wondering if it might have. I metered the center pin of the ISM harness and am getting 11.26V at the pin and only 3.38V on the right pin.

You need to make sure your car is warm when reading dwell. Sounds like your o2 sensor was still in open loop.

[DeLorean937]

I miss typed, the needle does not sway just stays pointed straight at 60 does not make a difference when adjusting. Read dwell and adjusted at operating temp.

[PJ Grady Inc.]

ISM seems like its buzzing with the microswitch pressed and the flap is closed. When I depress the microswitch it opens about a 1/4 of the way. I got a dwell meter and hooked it up when running the car I connected the lead of the orange wire and the other to ground. The needle does sway like ive seen in videos but rather just stays pointed at 60. Makes no difference when I adjust the mixture. 02 senser is hooked up and FV is buzzing.

I read a post where a ISM can short out the Lamba ECU so I was wondering if it might have. I metered the center pin of the ISM harness and am getting 11.26V at the pin and only 3.38V on the right pin.

A good basic test of the ISM and the ICU that contols it is to unbolt the ISM but leave the electric connector attached and turn the key on while observing the rotary valve operation. If the system is sound it will open completely and then gradually close down to an 1/8" slit or less over the span of about 23 seconds. This is a pretty consistant SOP if the system is sound.
My guess is most of your troubles have to do with the fuel and ignition items already mentioned as well as your self inflicted CO adjustment but there are methods to get you back in the ballpark if you haven't already done so. Also make double sure your dwellmeter is hooked up correctly or you'll get strange readings.
Rob

[dn010]

To read dwell I stuffed a bent cotter pin down into the back of the connection and hooked to it there, the other side to ground. Can you confirm you've got tight, clean bulkhead connections? Clean grounds? No vacuum leaks?

[Ron]

It helped a little bit by lightly seating them.Close the brass fittings all the way.


But I was wondering if the micro switch is depressed when cold, is the idle speed motor suppose to open all the way?Depends. With engine off, throttle off, and you first turn the key on, yes, initially...(As Rob described). Other times the ECU determines the position depending on the temp/RPM/... It varies...


I miss typed, the needle does not sway just stays pointed straight at 60 does not make a difference when adjusting. Read dwell and adjusted at operating temp.This is a symptom of a defective Full Throttle Switch, Thermal Enrichment Switch, and/or short along the Light Green wire connecting the two to the Lambda ECU. (Full Throttle micro very common). Check out D:04:15 in the workshop manual, when you get all of the other things worked out.

[DeLorean937]

Thanks for all the help guys. I checked everything you mentioned and I think I got the car running a lot better. Now I have to check the automatic kick down cable as now the car wont switch gears until very high RPMs. Should this cable be back out all the way out tight or should the cable be on the looser side? Also, just out of curiosity, would the auto shift computer/governor cause poor running symptoms? It is still the original unit.



Close the brass fittings all the way.

Depends. With engine off, throttle off, and you first turn the key on, yes, initially...(As Rob described). Other times the ECU determines the position depending on the temp/RPM/... It varies...

This is a symptom of a defective Full Throttle Switch, Thermal Enrichment Switch, and/or short along the Light Green wire connecting the two to the Lambda ECU. (Full Throttle micro very common). Check out D:04:15 in the workshop manual, when you get all of the other things worked out.

[David T]

Thanks for all the help guys. I checked everything you mentioned and I think I got the car running a lot better. Now I have to check the automatic kick down cable as now the car wont switch gears until very high RPMs. Should this cable be back out all the way out tight or should the cable be on the looser side? Also, just out of curiosity, would the auto shift computer/governor cause poor running symptoms? It is still the original unit.

If you have an automatic transmission you should do all of the external on-car checks and adjustments as outlined in the Workshop Manual G:05:01-:03. I would also add checking the vacuum line to the modulator, the wires to the shift computer (get them secured and away from the exhaust pipes) flush the oil and replace, and clean the filter. If, after proper adjustment, you do not get forced downshifts, you probably have to repair or replace the shift computer. Check the fluid level as per G:04:02.

[PJ Grady Inc.]

Thanks for all the help guys. I checked everything you mentioned and I think I got the car running a lot better. Now I have to check the automatic kick down cable as now the car wont switch gears until very high RPMs. Should this cable be back out all the way out tight or should the cable be on the looser side? Also, just out of curiosity, would the auto shift computer/governor cause poor running symptoms? It is still the original unit.

As David T suggested you should perform the automatic adjustments as per the workshop manual. A bad governor can cause late upshifts but would not affect engine performance directly. It will affect acceleration greatly however when it causes the transmission to start in L2 or drive. Very late upshifts are almost as damaging so you'll want to find the cause ASAP. How many miles does the car have(if we can assume no broken angle drives or cable disconnects in its past)?
Rob

[Ron]

+1 especially to do ASAP!

[DeLorean937]

So I looked everything over and it drives and shifts perfect .. that is until I get on the highway. There's no problem with shifting, but when I get on the highway and up to speed it's fine, but when I slow down on the off ramp to a compete stop it wants to die and has no power. Almost like it goes out of adjustment each time. I power the car off and leave it and restart a few times it gets better and back to driving perfect in the city. Would the ISM motor hang open or anything? Any ideas?

[PJ Grady Inc.]

So I looked everything over and it drives and shifts perfect .. that is until I get on the highway. There's no problem with shifting, but when I get on the highway and up to speed it's fine, but when I slow down on the off ramp to a compete stop it wants to die and has no power. Almost like it goes out of adjustment each time. I power the car off and leave it and restart a few times it gets better and back to driving perfect in the city. Would the ISM motor hang open or anything? Any ideas?

The symptoms you describe seem to change drasticaly with each post which tends to skew any advice all over the map! This is a car with multiple issues perhaps? If you haven't already been there it's time for a peak into your fuel tank to look for trouble.
Rob