87 mustang gt surging idle/stalling

Check the timing , with spout unplugged see what the timing is set around. Spout is a plug near the distributor wire harness. I would set it around 14 deg. Super Unleaded, 13 deg Plus... Every car is different. Set it high , if it pings back it down a degree, if it pings after that back it down another degree and so on till you find your cars sweet spot. Of coarse type of gas you run effects this.

Cheak the fuel filter and fuel pump. Normally a bad fuel pump humms really bad.

Check you Map Sensor , make sure that the Manafold vaccume line is hooked up to it and that it does not have any holes in the line. 87-88 really depend on the Map sensor. MAP sensor is mounted on the firewall on a bracket near vaccume tree.

Replace the Temp sensor, the sensor that lets the computer know what temp the engine is. (not the temp sending unit) Check or replace the sensor that that is screwed into the black tube that runs under the throttle body to the heater hoses. Sensor costs around $30.00

Have you replaced to O2 sensors?

What does the motor idle at?

Disconnect the vaccume line that goes to egr and see if it changes anything. Plug the vaccume line with your finger after you dissconnect it.

Have you checked the fuel injectors to see if one may be plugged or leaking (bleeding off pressure) ?

I cases like yours, it is best to go through a proccess of elimanation. I have no doubt that the problem you have can be fixed, the comment that the mechanic made was a cop-out. If he really knew what it was or knew how to fix it he wouldnt have said that.

Dont feel bad everyone that has had a fox body has gone through the idle surging bs, Keep looking and you will find it.

One last thing I just thought of. What temp themostat was installed? If it was too cold of a thermostat like a 160 that would make it surge.

Let us know !!

The timing is set at 13 deg. I use reg. unleaded gas. The fuel pump was replaced about 6 months ago and the filter was again replaced 2 days ago. All of the vacum lines on the carhave been replaced and all of the ones going to the map sensor are good. How do you check the map sensor? I have not changed the temp sensor, but will doso this weekend. The o2 sensors were changed last year. The engine idles at about 800 rpm with the air off and when it stops surging it idles at about 900-1000 with the air on. The thermostat is 180 deg. I have not checked the injectors. I will do that this weekend as well.

Thanks for your response

At first thought it sounds like a vacume leak. Are you hearing any type of sucking noise from any of the hoses?

Any help would be apprieciated Well stupid me for not reading the whole thread. Since you have replaced all vacume hoses have you had the fuel pressure regulator tested to see how much pressure you are pumping? Ford uses a closed fuel delivery system to the engine and back to the tank. The fuel pressure regulator delivers fuel to the injectors, if the pressure is low boost is compromised. Any dealer or Firestone or garage can check the pressure for you.

very thorough ... and that mechanic is a lazy idiot.

the idle bypass valve itself may be clean, but the valve and/or ISC motor may stick... this would be the first thing i would look at.

you adjusted the tps to the right voltage but was the throttle stop adj screw at the right point when you did it? warm engine and disconnect (key off) idle control sol and set it to idle at 550 or 600 rpm.. or 50 below nominal

block and disconnect all vacuum lines to accessory parts, incl heater.

run vac leak test on those and power brake booster vac.

vac gauge on egr valve actuator, see if engaging, on and off.

check egr flow, vac directly to actuator to see change in engine when vac is applied - tests flow and ops.

block thermactor air to manifolds, to see if it affects the problem.

Thank you for all of your responses.

The air bypass assembly is new and i believe it is working correctly.

I adjusted the tps after adjusting the throttle stop according to one of the threads posted for it is not in any of my repair books.

Which solinoids are for the idle control, and how do you adjust the idle on the car. I thought and read that it was computor controled.

I did a vacum check and found that there is no vacum coming from the egr solinoid, but there is vacum to the solinoid. So i have ordered a new solinoid and it should be here in a week.

Again thank you all for your help

I will post a follow up when the new part comes in

Look into a engine idle air kit part number F2PZ-9F939-A. It goes between the idlemotor and the spacer.

Hi group,

Thanks for all of the replys.

I have got the car running pretty decent right now.

I replaced the egr vacum solinoid and the car is idleing pretty steady at about 800 rpm with or without the air on.

The only problem im having now is that the car will stall the first time i start it, once i restart it will run fine until the next time i try to restart.

I am having the fuel pressure check to day and hopefully this will solve the problem if parts need to be replaced.

I have a couple questions and hopefully someone can tell me the answers.

What is the correct idle for this car, i have read several different specs and they seem to range from 600-900 rpm.

How can i adjust the idle if it is indeed lower than what it is running at. Will the idle air valve spacer do this?

Again thanks for all of the help.

Chris