1991 C2 964 surging problem
 

I have a very annoying problem with surging with my 91 964. The car runs fantastic except for the following:

In first or second gear slowly going up a slight grade starting at around 1800 RPM’s it begins to surge and continues to get worse through 2100 RPM’s and then begins to back off and is completely gone at 2600 RPM’s.

The car is a 5 speed with a stock engine and I have done the following to try and fix this issue with no success.

I have replaced the following:
02 sensor – all fuel injectors – Reference sensor – head sensor – DME – Dist caps – rotors – dist. Belt.

I have checked – cleaned and where possible adjusted to factory specs, the following:

Throttle body plate
Spark plugs
Air flow meter and voltages
Air Filter
Fuel filter
Fuel pressure (cold – hot and driving)
C0 at idle and while driving
Checked – cleaned all grounds
Throttle switch
Smoked checked for vacuum leaks
Alternator output
Cat converter
Multiplug connectors

I have even ran the car with the 02 sensor disconnected.

Any suggestions – help you can provide would be greatly appreciated.

Stan

Try running a couple bottles of Techron or Gumout Fuel System Cleaner through it. Don’t bother with the $1.99 cleaners at Wal Mart, or even the weaker Techron Fuel Injector cleaner. Use one of the good ones. Or, try a good ol’ Italian Tune-up. See if it makes a difference.

How many miles on the car?

Edit:

I should add this: What the heck are you doing at 1,800 RMP going up a hill? These cars want to be >3,000 if at all possible.

I have run many bottles of 503 through the fuel system, and how about speed bumps !

What’s 503?

Sure, you need to be at really low speeds to go over speed bumps, but also in first gear.

When you said slowly going up a grade, I didn’t think you meant speed bumps. If you’re going up a grade at 1,800 RPM in second, I would think you’d want to be in first instead.