Matt Daniels

My '86 4kq has been <a href="https://forums.audiworld.com/4000/msgs/178337.phtml">stalling</a> when I clutch-in at speed.

I've cleaned the ISV, looked for (and repaired) vacuum leaks and just replaced my coolant temp sensor, nothing has had a real effect, but replacing the sensor may have made a slight improvement.

On the occations that it doesn't stall, the RPMs will drop real low and almost stall but then catch itself and idle normally. It's done that almost the entire time I've owned the car. Although, I'm thinking that may have started when I cleaned the ISV shortly after I bought the car.

Even though I've cleaned the ISV multiple times, I'm wondering if it still may be the problem. Possibly it's gone bad to the point where cleaning it doesn't make a difference any longer? Any way to test it to see if it's operating properly?

Any other suggestions on what could be causing my stalling problem?

PartyBoyRacing

Any cold start or warm start issues?

Matt Daniels

One other thing I forgot to mention - when cold it doesn't appear to do the stumbling/stalling issue.

Of course, it only takes a few minutes before it gets warm enough and then it starts, so hard to really diagnose that it doesn't do it when cold.

PartyBoyRacing

I suggest using the following test to rule out or confirm problems with the following sensors:

- Coolant temp Sensor unit (in coolant supply hose near front of cyl head - top one)
- Coolant Temp Sending Unit (in coolant supply hose near front of cyl head - bottom one)
- Cold Start Thermo Time Switch (in rear of cyl head)

Simply pull each connector separately during different phases of operation (start-up, cold operation, and warm operation) to see if anything changes (I do it at idle and under load just to be sure)

If you pull the connector and the performance changes...then it's probably working.

If you pull the connector and the performance does NOT change...then it may not be working.

If that doesn't get you anywhere, then it's time to pull out the multimeter.

Just FYI: The ECM uses the info from both the coolant sender and sensor to determine the proper air/fuel mixture. The car can still run if one fails, but if both fail you'll know it. It'll still start with a lot of gas pedal manipulation (have to get it in just the right position), and run very poorly (have to keep the RPM up or she'll die).

Thus; if you pull either one of the coolant tempurature Sensor or Sender and your car has a really hard time starting...good clue that one of those two are bad.

Matt Daniels

I generally check Autohauz AZ for my parts. Don't see anything listed as a thermo-sensor, although there are various temp-related sensors &amp; switches available.

PartyBoyRacing

Just using generic term for the heat sensitive sensors/senders...check out the thread below.