I have tried everything in the world to try and fix my cars acceleration problems. Its an '88 TII with a full turboback and intake. I just recently put the engine in the car. It has an S5 engine with S4 wiring harness and ECU. Also the TPS and fuel injectors was from the original S4 engine. At lower RPMs lower than 2500 RPMs when trying to accelerate the engine will vibrate. More like a side to side shaking. The car also idles high around 1200 to 1300RPMs and when idleing also has the vibrating from side to side problem. At any rpm above 2500 the car accelerates fine with no miss or vibration. It runs a steady 7lbs of boost and has no vacuum leaks. My boost gauge shows about 15 or 16lbs of vacuum. I'm not sure if this is caused by bad motor mounts or a running issue. The mounts seem to be in good condition. The TPS has been adjusted correctly also. Any ideas would be great.

 

did you test for vacuum leaks?
www.fighters-garage.com has a tester that is Cheap,.and it saved Me Bigtime when I had to diagnose my car.

 

I have checked for vacuum leaks 2 or 3 times now just to make sure and there aren't any. The problem just seems to have no solution. I will check for leaks again tomorrow just to make sure though.

 

Which emissions harness did you use? Was it a turbo emissions harness or an N/A emissions harness?

 

No vac leaks on the car. Turbo harness. The car was an S4 turbo but has an S5 engine. I used the S4 TII harness already in the car and the TPS and fuel injectors from the old S4 engine and switch them to the S5 engine.

 

Have you ruled out the the Boost sensor as being problematic? Just disconnect the vacuum hose to the sensor, plug it, disconnect the TPS and take the car for a ride and see if it behaves differently.

 

sounds like bad motor mounts. maybe i'm thinking too simple or maybe it is that simple.

 

Hm..... Try cleaning out stuff? TPS, AFM, BRS, primary injectors, etc.

A way to check and see if it's the AFM by idling the car, with the AFM and TPS disconnected. When it revs through the problem zone, on the tach, there should be a very noticeable change. If not, then you've found your problem.

 

I tried disconnecting the boost sensor to see if that helped but it didn't change at all.

I will try the AFM to see if that is the problem. The TPS is good and adjusted for sure. I actually disconnected it the other day and drove it thinking it may make a difference. What is BRS?

 

Boost Reference Sensor.

Make sure you use a cleanser that is 'Sensor Safe.'

 

Put the car in gear with the hood up and accelerate slightly. If you see the engine lift excessively, you have your answer. Don't forget to this only checks one side. You will have to put it in reverse and repeat to check the other side. As far as the high idle. Could be a faulty or stuck idle air control valve or a vacuum leak. Remember, the vacuum leak doesn't have to be at the engine. It can be at the other end of the vacuum line coming from the engine. Ie, sensors, brake booster, or even a/c system.

 

Did you at least try to tighten the motor mounts down? You'd be surprised...

 

most problems arise at the upper RPM range or while in boost, for example, so i'm hesitant to think it's more than just the mounts.

 

Course, the ethreal cure-all for vac-leak finding is carb-cleaner.

With the engine idling, shoot a little bit around the rat's nest and known vac-line termination points....

DO NOT FOG THE ENGINE BAY

This **** WILL light if your exhaust manifold is hot!

You'll know if you find a leak when the tach either drops or jumps (depending on the mixture in the spray.

I've used this and the starting fluid method a million times on every kind of engine imaginable and it works. Try it and if there isn't any reaction - and you've done it right, then the vac-leak problem doesn't exist and you can debug, elsewhere.

 

It sounds stupid but you're using the s5 tii flywheel on the s5 engine and not the s4 one correct?

 

Thanks. I wasn't sure what you meant but I have checked it and it made no difference.

I will try putting the car in first and reverse to see if that may give me my answer. Thanks for the suggestion, I hadn't thought of it honestly.

I've tightened them so I know they aren't loose that's why I thought they my be worn.

The problem is actually in the lower RPM range. 2500 RPM and below is where I'm experiencing the problem. Anything above that range seems great.

I've tried that twice now and come up with nothing as far as a vac leak goes. I've checked, checked, and rechecked that just to make sure because I thought that was the problem too but it wasn't.

No, I haven't switched the flywheels. It still has the OEM flywheel and counterweight that originally came on the s5 engine.

 

I cleaned the sensors and AFM today and it didn't solve the problem. I double checked the engine mounts today also and they are tight and the vibration is still there. When the car is idleing the engine also vibrates and moves from side to side but had no miss and is still completely smooth above 2500 RPM. The only time it vibrates below 2500 RPM though is when I try to give it gas to acccelerate or maintain constant speed. When idleing and revving down it is smooth just under acceleration. Could worn transmission mounts and brackets cause this?

 

Possibly, may I also suggest that you check the exhaust too, ensure there are no leaks, especially around the cat. If you want to absolutely 100% determine there are no vac leaks, use a tester like the link above that hooks up to the turbo inlet, then with a press. regulator up to an air compressor.

 

The exhaust doesn't have any leaks or a cat haha. I will get a tester and pressurize it to see how that goes. I'm running out of ideas haha.

 

Have you bypassed the fuel pump relay resistor to see if it is possibly the quirk in your system?

 

Out of curiosity have you checked everything? Timing off, tps adjusted correctly?

 

How would I check this?

I have adjusted TPS correctly and the timing was perfect when I checked it. Adjusting the TPS made no difference.

 

Disconnect the four wire plug and jumper Blue/Red to Blue.

 

Ok. I'll check it after I get off work or first thing tomorrow. Thanks.

 

I haven't had a chance to do this yet, but I am going to try and check it out this evening if time allows. Just a quick question. When I do this and drive the car what should I be looking for?