Hey guys a buddy of mine has a bone stock '94 A4 with 77K miles. It is a well kept car, and runs great most of the time. However once in a while the car will run hot (say about 235* or 240* normal is about 205* for this car) and will start surging while stopped and in drive and It will rev to almost 2K RPM by its self. It also has an extreme amount of hesitation/stumble when it starts running this hot.

My only suggestion would be a sticking thermostat. The radiator is very clean inside and full obviously with no leaks.

I hope you guys can help.

 

This sounds close to the issue I am dealing with right now.
Mine has started to do it more often, it runs great for about the first 1/2 hour but when everything warms up the idle when you stop at a light will jump up to about 1600 or so and come back down then go back up but if you put it in neutral it will idle fine. I brought it to a shop last week I could not take it any more. Here is a list of things I did that did not work to fix the issue.
New TPS
New IAC
New Coil
New fuel injectors+ regulator
New Plugs
New Plug wires
Cleaned throttle body
Cleaned radiator
Could not find any vac. leaks
No codes

 

did you change the rad cap and thermostat?

 

When the new 388 I built for my 96 started doing that a week or so ago, I - at first - didn't pay it much attention, since it's been so HOT here in TX.

One evening, on the way home, the temps began to climb and kept on going up. When they crossed 250F I pulled over and checked that both fans were on - they were.

By then temps had hit 260, warning light came on and I could hear the coolant boiling. I shut down the engine and found a restaurant to have dinner while I waited for the engine to cool.

After an hour of so, I fired it back up and barely made it home before the temp again hit 260F.

Next morning I used my Prestone Coolant tester and found the coolant/water mix was right on. I then pulled the stat and replaced it with a new 180 stat from AutoZone.

Problem solved.

While there, I ordered a Fail-Safe Stat part # 7307-180 and when it came in I installed it replacing the new one I'd just installed.

Result, stat began to fail in a gradual manner before it finally died. When it did, it died in the closed position, hence the over-heating.

So what I'm saying is if you're getting an intermittent over-heating problem be sure to change the stat to a Fail-Safe one. One that, if it fails, will do so in the OPEN position.

Jake

 

Thanks guys for the help. Is the stock thermo 195*? Would changing it to a 180* make it run rich or cause any other problems?

 

My 96 LT1 has a 180F stat. Going with a 180 won't cause any problem. It probably won't make the engine run any cooler - without reprogramming the fans to turn "ON" at a lower temp - but it won't cause any problem like running rich.

Jake

 

Sorry to say, but I had the same problem for months....changed all the things mentioned above, even the knock sensors, to no avail. Changing the Opti cured all my ills.

 

You should have a coolent sensor on the drivers side front of head.If the car has been overheated that can cause a rich problem.