I have a '95 C2 that's started hesitating during warm-up. The car starts just fine, and runs great at first. It's after warming up for maybe two or three minutes that I get no initial power. Idle is fine (maybe a little lopey), it's just that a normal take-off, letting off the clutch and easing the throttle gives no power. I can rev the engine and finally get going, but nothing close to how it should be. After another few minutes, when the car is warmed up, it goes back to totally normal.

It's completely stock and coming up on 90k. I just did the plugs and air filter (have the fuel filter left to do for that service) over the summer. This just started happening in the last few weeks. I'm in the DC area, so the temps were in the 50s today.

Any ideas where to look?

Chris.

 

I would suspect the ignition system: Spark plugs, wires, distributor cap, distributor rotors, etc.

When this happens, is it wet? Rain, or other moisture?

/

 

Might just install that Fuel Filter now - ELIMINATE IT >l and get that out of the way

 

tation
All of these are due for replacement, if not already done at 90,000.

 

Yes, ignition or fuel filter.

Ignition can cause this by a cylinder not firing results in extra unspent fuel in the intake influencing mixture and so the proper burning of the fuel.

Same goes for fuel filter as with increased throttle demand with a clogged filter starves the engine off idle

A third cause is debris in the gas tank clogging the fuel path although this is very unlikely as our cars do not have steel tanks.

PS: A vacuum leak can also cause this issue and the vacuum actuators on our cars are old and may have cracked diaphragms that leak. There is an easy testing procedure for checking these:



https://rennlist.com/forums/993-foru...naware-of.html

 

I would do the caps and rotors first and see if the issue is resolved as they seem to have a lot shorter service interval before causing ignition issues. They are also the least expensive and easiest to replace, then wires then plugs. All the issues described above should throw an OBD Code such as "emissions relevant misfire". If no codes are present you may want to look for a vacuum leak at one of the vacuum actuators as a large leak can be an issue and not throw an OBD code.
Andy

 

Update -- I've done the plugs, caps, rotors, and fuel filter and I am still getting hesitation and even the occasional backfire during warm up. The car starts fine, and it runs fine when warmed up, it's just that hesitation during the one or two accelerations from stop in the first five minutes or so. I don't drive the car very often, probably less than 500 miles a year, and put new gas in it last weekend (it was down to less than 1/4 tank).

I used a vacuum pump at various locations (front and rear) and everything seems tight -- no vacuum leaks I could find.

I used the gas pedal method of pulling codes (it's a '95) and got what I think is one flash then five flashes, which I think is no codes stored.

Anywhere else I should look?

Chris.

 

Clean the Idle Stabilization Valve. It's easy to do, may need cleaning anyway, and eliminates one more possible cause.

Bruce7's usual incredibly detailed DIY here: https://rennlist.com/forums/993-foru...valve-isv.html

 

Just out of curiosity, have you ever replaced your O2 sensors? A 95 has two of them, and as they near their lifespan they get slow and lazy and can produce the types of symptoms you are reporting.

However, my thoughts on the potential issue mentioned above should be reported through your OBD1 computer system.

You could be right at the threshold where the O2 sensors are not reported as faulty by the OBD system, but are slow in responding, which may account for the car running well, once it's warmed up.

P.S. You might also want to buy a can of MAF aerosol cleaner and try that first...

If it were me, I would see about borrowing a decent generic OBD1 scanner. The Actron 9580 model I have, produces real-time voltages of the O2 sensors.

HTH

 

Did you replace the ignition wires?

I would also run a can each of Lubromoly Ventil Sauber & Jectron in the fuel as that oftentimes makes a big difference.

 

You mean one of them. Bosch lists this one with a "change interval" of 160,000 kms (99K miles). Not saying that is the issue, just posting what Bosch stated. It is a 4-wire unit which means it does have a heater.

Easily tested with an oscilloscope if you have one.

 

This is great information -- thanks. Since I have just under 90k, I think I'll start with the oxygen sensor, then MAF cleaning, then plug wires. Both the oxygen sensor and plug wires are original to the car.

Based on how the hesitation comes on and ends, the oxygen sensor makes the most sense to me.

Thanks again,

Chris.

 

Chris,
You might want to start with the least expensive first.
The MAF aerosol cleaner, O2 sensors, wires; in that order.
Try one, check results; try the next, check results...You get the picture. This way you isolate the variables and pinpoint the fix.

 

It was the oxygen sensor. Replaced that and warm up is normal again.

Super easy to do on a '95, didn't even have to jack up the car. Most difficult part is removing the plastic cover that hides the connection in the engine compartment.

Chris.