94 Villager Engine Surge

[MTHiker]

We had the knock sensor replaced on our 94 Villager. It has 198,000 miles. The engine had little power and our mechanic said the sensor was bad. The power is back, but as soon as the rpms hit 3,000 they drop immediately to 2,000. Then suddenly go up to 2,500, then 3,000, then back down to 2000. The surging is all in increments of 500 rpms. I experience this on the freeway trying to maintain a steady speed. On city streets, it just feels like it is shifting gears hard as I cannot see any drastic changes in the rpms. The mechanic changed the fuel filter and cleaned the master air intake(?). It cost a small fortune to replace the sensor. He tells us the fuel pressure is good. Any ideas? Thanks for any help and advice.

[tempfixit]

Originally Posted by MTHiker

We had the knock sensor replaced on our 94 Villager. It has 198,000 miles. The engine had little power and our mechanic said the sensor was bad. The power is back, but as soon as the rpms hit 3,000 they drop immediately to 2,000. Then suddenly go up to 2,500, then 3,000, then back down to 2000. The surging is all in increments of 500 rpms. I experience this on the freeway trying to maintain a steady speed. On city streets, it just feels like it is shifting gears hard as I cannot see any drastic changes in the rpms. The mechanic changed the fuel filter and cleaned the master air intake(?). It cost a small fortune to replace the sensor. He tells us the fuel pressure is good. Any ideas? Thanks for any help and advice.

How he determine that the knock sensor was bad??

Check for DTC codes.

Possible throttle position sensor, distibutor problem. You may need to hook it up to a scanner to read all the engine data.

I don't see how the knock sensor being replaced will help anything as they very rarely are faulty in these vans.

Send me a PM with your email address and I can send you some instructions on how to do some diagnostic testing and retrieve the codes.

[MTHiker]

Thanks. The codes were checked using a hand held scanner. Here is the most interesting thing, if I take off the overdrive, the surging stops. Could this be some kind of electrical problem connected to the major engine work of replacing the knock sensor? As you indicated a throttle position problem? The scanner indicated the the knock sensor was going bad back in August. The power continually diminished over time so we thought it was time to replace the knock senor.

[tempfixit]

Originally Posted by MTHiker

Thanks. The codes were checked using a hand held scanner. Here is the most interesting thing, if I take off the overdrive, the surging stops. Could this be some kind of electrical problem connected to the major engine work of replacing the knock sensor? As you indicated a throttle position problem? The scanner indicated the the knock sensor was going bad back in August. The power continually diminished over time so we thought it was time to replace the knock senor.

The mechanic must have cleaned the MAF (Mass Air Flow sensor). When you look at the air cleaner housing do you see the air filter element? Reason I ask this is that these earlier Villagers are known for the housing to warp exposing the filter element thus the MAF is getting unfiltered air which is contaminating the sensor causing improper air flow and causing your lack of power. Thus the cleaning of MAF sensor has improved the power issue.

Have you had the codes rechecked since the Knock Sensor replacement?

Yes it is possible that a wire is not properly connected or loose, double check all connecters.

Usually a knock sensor code is triggered by another code which is the cause of a vibration of some sort in the engine that the knock sensor detects and sets a knock sensor DTC.

Sounds like the torque converter lockup is not working properly when in overdrive.

Again check for DTC codes and post them and will go from there.

[tempfixit]

Check your upstream oxygen sensor also.