idle surging
 

86 944 n/a

I have been experiencing an idle surge when care gets to temp. Idle goes up and down.
I pulled off the intake and replaced all the majar hoses(vac). I checked the other hoses and they all looked fine.
I replaced the idle control valve ( new)
I also replaced the engine temp sensor and the large air intake j style hose.
The injectors were cleaned and resealed. The fuel regulators have been replaced as well.
Everything put back and car started right up ( surpise). Car still surges.
What next? Car did this before the work.
Any idea's.
:confused:

sounds like perfect symptoms for a bad throttle positions sensor.

That was my next venture. I have an 87 that idles fine. I was thinking of taking it off and give it a try before i pluck down the 75$ or so for a TPS.

What else might it be?

I installed a new throttle sensor. Followed Clarks procedures.
Still surging.
Any new ideas?

O2 sensor comes into play when engine reaches temperature, but I thought the surging caused by a faulty O2 sensor shows up during steady part-throttle driving.
How about the AFM? Try swapping with your "donor" car to see if that clears it up.

swapped out the AFM . Surge still there but not as pronounced.
I removed the plug from the throttle sensor and the car stopped surging but idle increased a bit. What does that mean?
I have re-checked the vac lines - this time squirt water(soap) to see if any leaks. Nothing I can find.
Help

About the only thing left is the DME. Do you have a fuel pressure reading? It could be a weak fuel pump however they tend to work or not work but it could be the fuel filter doing it. Has it done it on several tanks of gas? Poor gas could also do it. You also mentioned you replaced the engine temperature sensor, what about the temp sensor on the radiator...or is that the one you replaced? Instead of soap and water, you probably need to try something like WD40 or starting fluid and see if rpms go up when sprayed on a particular location. Try to eliminate fuel by getting a good fuel pressure reading. After eliminating fuel, then let's try to eliminate voltage leaving vacuum and timing. You have definitely done a lot to try and find this.

I will try the alternative to water and soap. The question I have at the moment is if I remove the plug from the TPS the surge goes away. If it was a fuel issue, wouldn't the surge continue. I am speaking from inexperience here so be gentle. Also if it was a fuel issue wouldn't it be from start up and not just when it hits a specific warm temp.
Again I am speaking from inexperience but it sounds like something is ready something incorrectly and only at temp.
Does the plug from TPS go to a relay or straight to the main puter?

oh yeh, the sensor I replaced ( temp ) is the one on the block and not on the radiator. It was my understanding that this sensor allows the puter to know what temp the engine is. The one on the radiator allows the fans to kick on ??

Yep, you are right about the fuel. If it were that, it would probably do it all the time. I don't know WHAT I was thinking? :) Sorry bad suggestion there.

No problem. I am not sure what the issue is. I was thinking about swaping the DME out with the one in my 87 and see what happens. if that does not work I will take everything apart again to see if I missed something. I have removed everything twice to double check lines etc and so forth.
I am still confused as to why when the plug to the TPS is removed the car does not surge. Somewhere that plug ( I am guessing at this point ) is getting an incorrect reading.

I will wait and see what further suggestions I get. keep em coming. The only bad suggestion is no suggestion.

The more I think about it, I keep going back to Nynor's suggestion of the TPS or possibly the DME. Did you do the electrical tests on Clarks-Garage against your TPS? Did you adjust it per the instructions on Clarks-Garage? Since you can unhook it and it stops, it has to be related to that part or the DME itself.

If I understood clarks procedures, when installing the TPS I was to mount the TPS. don't tighten until it stops ( when turning). They tighten. I should then hear a slick click as the throttle opens. It aligned with the previous TPS. I heard the slight click as the throttle opens. The click is heard almost immediately.I hope I did that correctly. While I had the throttle body off I cleaned it as well. I checkd the large seal on the intake side and it appeared to be okay. sound right?

There are two temperature senders on the block. The one with the single spade connector is for the gauge only. The one with the blue socket is for the DME. Which one did you replace?

Blue socket. Believe in the area of the intake boot.

Sounds like you set it pretty close to right, did you check the wide open setting? Did you get the volts readings you were suppose to on the DME wiring harness?

I Just recently put an 87 dme and LATE style AFM(85.5) and i had a bad surge at the beginin. When i would disconect the AFM it would be fine. This is all at cold temp btw. I adjusted the screw on the throttle and for the most part it went away. Perhaps Cleaning the conections to the TPS sensor with some Electrical contact cleaner may help to get rid of anythink preventing a good conection.

Did you go through the proceedure to set your idle? Use the jumper to disable the IAC motor, then adjust to the proper RPM, then remove the jumper?

The only other issue I see is O2 sensor. They can cause this symptom.

waht about cleaning the connections at the AFM? (and every other connection you can find under the hood...)

Yeah, I've done that twice, Once a few months ago i forget the other time
Dme Temp, Fuel injectors, TPs, Afrm, Engien Temp, Oil Sender, engine Grounds, Ref Sensors, Just about everything i could see.

The Dme did help with less vibration when my Engine idles low. sometimes 500rpm now. The 83 DME and AFM idled reay hard at only 700-800rpm.