Poli84

I've been having hunting idle problems for a while and a cold start issue where the car would never start first crank in the morning.

I've cleaned the ISV twice before so was moving on to another item to diagnose.
Off a couple of recommendations I pulled the O2 sensor.
Drove home from work last night without the O2, ran well. This morning I disconnected the negative terminal to reset the DME while the O2 was still out.
Car started first crank but idle kept jumping from 800-1000RPM.

Took off slowly and it stalled. Every time I gave it some revs, started then stalled, repeat.
Plugged the O2 back in. Same problem.
Disconnected negative again while the O2 was still in, same problem.
Disconnected negative again, changed the DME relay, same problem.

What I have done and where to from here?

Earlydays

Vacuum leaks can be another cause of your problem.....

Poli84

That could be the cause of the existing problem but what have I done in the last 12 hours to make the car now undriveable?

Mr.Alex

Did you end up replacing the ISV or just ended up cleaning it? I had similar issues when my ISV was fully dead. Would stall on start up unless I gave it gas, and would run poorly while I was giving it gas.

Poli84

Just cleaned the ISV for now.
It is on my list as a potential to replace however, i wanted to eliminate the O2 being the fault first, hence why I disconnected it last night as a form of trouble shooting.

Once I get the car running again, I will replace the ISV... just need to get the car running again!

Mr.Alex

Would be great if you could find a local member to just swap it out and try another ISV. Seems similar to when mine was dying. At times it would work, then would idle fine for a sec till RPM rose to 1200 on its own and then die. After a while it just died on start up unless I kept feeding it gas.

Poli84

It wasn't running great until I unplugged the O2 and the negative terminal but it wasn't doing what it is now.

My ISV might be on its way out and need replacing but I have done something to something for the car to be now undriveable.

lateforlunch

by disconnecting the battery you wiped the adaptation clean. You need to perform system adaption with the hammer.

Mixter

What about the fuel pump?

Poli84

Thank you, this makes great sense.
I'll see if my mech can do an adaption for me in the morning.
I was able to drive it around the block by keeping revs up so should be able to get it to the mech, fingers crossed.

I've also ordered a new ISV and O2 sensor in an attempt to resolve the problem for good.
Will test for leaks too.

Jacke2c

Use a 9 volt battery (or a small DC voltage power supply) and you can cycle the valve while in your hand... If it is dead, it won't budge. You can close/open it by applying the 9 volt battery to the two terminals.

speedbagger

fuel pressure regulator?

https://rennlist.com/forums/964-foru...-c2-964-a.html

Steve Weiner-Rennsport Systems

Fuel pump check valve. When these start leaking (internally), the fuel rails and FPR lose pressure after sitting overnight and it will not start easily, especially from cold.

Naturally, I'm assuming your head temp sensor has been thoroughly checked out.

Bertrand

It could also be the secondary distributor belt. It's a quick check.

Navaros911

I've gone down this road and plenty of things weren't working as it should be.

All the below were checked and or replaced:

Fuel pump (comes with check valve)
Air flow meter (and connection at back)
ISV
Fuel Pressure Regulator (made a big difference)
Spark plugs
Fuel filter
Distributor caps
Spark plugs
Spark plug cables (checked and tested)
Today I'm testing the coils and modules (something died last week)

The car ran a little better with every change, but overall kept getting worse. All these parts are over 20 years old and probably well outside of any testing envelope... just saying, you may have more than one issue stacked on top of each other. And the electrical issues can be intermittent.

The coils (or module) have been going bad over a period of 5 months now. I could never find the problem with it being intermittent.

Good luck.

PS. I have no O2 sensor... option 150 car