2000 Forester Bucks and Surges When Warmed Up

[Enforester]

This is a 2000 Forester Auto. with 143,000.  The problem started years ago on a long trip.  The car shifted down and then revved up to about 4200 rpm and then shifted up and back to 2900 rpm and then started the cycle again and again.  I tried manually shifting with no success.  My best luck seemed to be to be very easy on the accelerator although that didn't solve the problem completely.

 

Ever since, it will run fine at first but when it has warmed up, say about 8 to 10 miles, it will start this again.  It seems to have much less of a problem when it is cold outside--especially in the winter months.  We rarely drive it now except in winter.

 

History:  replaced fuel filter, knock sensor, both 02 sensors, alternator, coil pack, transmission filter and fluids--no difference.

Switched out TCU with another working one--no difference.  Removed fuse for AWD--no difference.

MAP sensor cleaned.

 

It has a "torque" binding problem in forward and reverse when turning at very slow speeds.  This is nothing new. 

 

My new mechanic wants to put a used transmission in it.  I asked him why because through all of this the transmission has not become any worse, mechanically.

 

I am at a loss.  I need some help.  Why would it do so much better in Winter and do well for the first 8 or 10 miles until it warms up in other months?  

 

Thanks.

[Fairtax4me]

Couple things come to mind, could be a bad MAF sensor. 99-2001 had some problems with those and there was a TSB concerning replacement of the sensor element.

Have you noticed a decrease in fuel economy?

 

Another thought is a bad TPS. Erratic TPS signal will cause erratic shifting.

Someone needs to put a scanner on it and check the sensor inputs.

[Enforester]

Couple things come to mind, could be a bad MAF sensor. 99-2001 had some problems with those and there was a TSB concerning replacement of the sensor element.

Have you noticed a decrease in fuel economy?

 

Another thought is a bad TPS. Erratic TPS signal will cause erratic shifting.

Someone needs to put a scanner on it and check the sensor inputs.

Thanks for the response.  I cannot find the location of a MAF sensor on my 2000.  Need some help.  And what is a TPS?  Thanks.

[Fairtax4me]

TPS Throttle Position Sensor

 

MAF sensor, if it has one it will be attached to the air filter box on the passenger side. Black plastic housing with a 5 wire plug on it.

Some of the 2.5s from that era had them and some didn't.

If it doesn't have a MAF sensor, it will have a MAP sensor bolted to the top of the intake manifold or throttle body. Small square dohickie with a 3 wire plug.

A bad MAP sensor can cause similar problems.

 

Your first post mentions you "cleaned" a MAP sensor. MAP sensors can't be cleaned. If they are covered in oil or carbon they generally need to be replaced.