As stated have 94 Z28 automatic with 103K miles.

Seems to run Ok when cool, but after running for 30 mins or so has a real problem.
Will run smooth at ~1200 rpm but if press gas pedal to accelerate; hesitates and judders like crazy (old kangaroo gas - type motion).
If you really step on the gas the rpm's shoot through to 3000+ and it takes off!

Also found that it will surge when at a stop light in drive - rpm jumps to 900-1000 and have to keep firm pressure on brake to stop lurch forward.

Any ideas on where to start looking for the cause?
Thanks.

 

It appears the car runs bad in closed loop mode, which usually indicates a bad sensor.
If service lite is lit, get the car scanned & see what the complaint is
If the service lite is not lit, then it becomes a SWAG.
Try the standard stuff first.
New spark plugs and wires (always a good thing), replace the ECT sensor (not the temp gauge sending unit), check O2 sensors & replace if bad, check ignition module, check ignition coil, go big time and change the optispark.

 

Thanks Z28Pete.
Have to be honest and say I am trying to avoid the 'change optispark' option due to cost.
In past 3 months alone have spent >$2000 on ball joints & front end repairs and then a new fuel pump.........another chunk of change like that and my mrs will have a cow!!!

Should have my scanner back from a mate by the w/e so I'll see what the readings are, though as of now there is no sign of the SES light.

 

lol, why's everyone avoiding lil ol opti? your car will run way better once you change the old one out, it may be timeconsuming and tight but its worth it.

 

I guess it is a bit of culture shock.........and sticker shock too!

I remember changing the distributor on my old Ford (UK) Capri 2.0 Sport - took less than an hour, easy to do from top, plenty of space to work - biggest issue was in reconnecting spark leads to plugs I inadvertantly open the jaws of the push-fit connection so lead fell off 200 yds down the road.

Found out on the Z - have to drop the engine half out and replace water pump! Not something I am prepared or capable of myself - hence huge labor cost!

 

I also have a 94 z28 auto.
SAME EXACT PROBLEM.
but i had my opti replaced when the when my water pump broke about 10k miles ago. i think my fuel filter need to be changed, i'll do that tomorrow.
Keep u posted

 

FWI VCP...have had new fuel filter and fuel pump but with no improvement.

Did you get new plugs and spark leads when you got a new optispark?

Maybe the ECT sensor as Pete mentioned???

 

yeah i did. just replaced the filter, haven't felt it yet. cross your fingers.

 

Any thought that it could be a transmission problem?

Have to admit that I had the then-local Goodyear-Gemini place do a transmission flush and fill couple of months ago - and hadn't noticed the problem before.

 

After reading your last post and rereading your first post, I would say that the TCC (torque converter clutch) is not releasing when it is supposed to, and keeping the torque converter locked. Could be that when the tranny was flushed some of the dislodged gunk is obstructing some valve body passages affecting the TCC valve. Is the service lite lit ??

The PCM does not order TCC apply in open loop, and could be the reason yuo don't notice the problem when the engine is cold.