Idle surge and cuts out

[Cobra18]

I have been experiencing a weird symptom here lately.

Deletions:
EGR valve
Salt and Pepper shaker connectors (unable to find anywhere)

Tests performed:
TPS is in spec
Air Idle control valve has been cleaned
MAF has been cleaned

Symptoms:

Upon start up the car will idle from 500-1000 and surge for a while and then eventually will idle at 750
Once I start the car and drive, it feels like it is loading up and then after about 30-40 seconds of driving, it will all of the sudden snap out of it and run perfect. This happens every time I shut the car off and restart it after 5 minutes or so. The car runs great low-mid- high range

Anyone have any ideas???

[Winchester]

Have you tried pulling codes?
I had a similar problem on my 91lx. At idle it would surge
& it would pop in the intake when cold. I found a very small
Vacuum leak & that corrected the problem I was having.
This website is great for keeping tract of the cars but falls very short
In the technical areas. This may or may not help you.
Good luck with your repair!

https://www.stangnet.com/mustang-forums ... st-4941716

[Cobra18]

There would be a ton of codes since there were a lot of electrical modifications. It has an A9L computer from a 91 SSP car. This all just started one day. Also forgot to mention that there is a bunch of pressure when I remove the gas cap to get gas.

It almost feels to me like maybe injectors leaking when the car is shut off and then has to burn the excess fuel out and then runs fine

[WillyB93]

The surge is probably the upper intake plenum gasket, try spraying some carb cleaner around the gasket area while running to see if it idles up. The gas tank will develop pressure, might check the venting tube and the gas cap.

[Cobra18]

I have sprayed the upper intake with carb cleaner and the idle never changed. My next step will be a new gas cap. Thanks.

[buddha]

What MAF does the car have on it?

[Cobra18]

F1SF-12B579-AA
AFH70-02
7L10

[69boss]

if you are confident there are no vacuum leaks and the iac and maf are ok and the maf is actually calibrated for the right injectors and tps is good also, then you can try to buy one of these and install on the iac it gives you a little more adjustment for idle control
this solved some of my idle issues of course my engine is anything but stock so....


https://lmr.com/item/LRS-9939A/1986-93- ... c-Adjuster

[buddha]

It sounds like it's only happening during open loop.................not using the 02 sensors for anything and is working off the internal mappings and with what the MAF is providing.

http://www.enginebasics.com/EFI%20Tunin ... %20o2.html

You see lots of guys with this issue, they will actually unplug the MAF while the car is running to determine how the car runs in limp mode. Do a little research on this, you'll find LOTS of posts on guys troubleshooting this.