I've got a problem with my brothers 1991 2 liter FI 4 cycle 3S-FE engine, manual transmission.

The car hesitates in 1st and 2nd on flat ground. With the clutch fully engaged the car hesitates and then accelerates roughly, then drives fine. This happens not every time from a dead stop, but intermittently.

Once the car gets on a hill, once the inertia up the hill has ceased the car has serious trouble. Once the clutch is fully engaged in 1st or 2nd it hesitates and eventually stalls if continued for 20 minutes uphill. If the car is stopped on flat ground for a couple moments and then shifted into 1st and aggressively accelerated it seems to not have the problem at least for a few minutes.


There are no error codes, I tested for error codes a few months ago and found a couple o2 sensor problems. I inspected and ran electrical tests on the 2 I could find and all the troubleshooting came up with good results. I cleared the codes and they have not returned since. I am getting the normal System Clear signal from the ECU.

I'm at a loss here, I don't know manual transmissions very well, and am not convinced this is the problem, It seems to be fuel or air related.
I am continuing my troubleshooting efforts, but have no money to start replacing random parts. I am armed with a digital multimeter and considerable working knowledge of vehicle repair.

Any suggestions will be greatly appreciated, I posted some solutions and advice in some other threads hoping to reciprocate some sound advice.
Thank You

 

Test fuel pressure/flow. Blocked filter, bad fuel pump. Not a solution, just what to look at.