Sputtering; Bad ISC; No Knock Sensor

[shrewmouse]

I just took my "stock" 92 Plymouth Laser RS Turbo AWD to the shop and they told me what I already know. The idle speed control motor is bad and the computer is complaining about the knock sesnor.

Because I had an idle surge problem I looked at the ISC motor. I could hear what I can only describe as bad electronic sounds coming from the Idle Speed Control Motor. After disconnecting the ISC the car idles about 2K. From what I've read, that is expected.

Here's the real problem:

When I put the hammer down and get to about 4.5K RPM the engine starts to hesitate. It seems like the engine is turning the fuel on and off.

As I stated earlier the car is an AWD Turbo which means that the engine should have a knock sensor on it. Well, it doesn't. That is why I put "stock" in quotes. I assume that the engine is not the original engine. Otherwise the ECU would be complaining about the knock sesnor.

Here's the question:

Will any of the following fix my hesitation problem?

• Replace the ISC Motor.
• Fool the ECU into thinking that there is no knock.
• Install a knock sensor.
• Something else.

 

[Royalty]

i'm going for
A & C

I've had the same problem

 

[PaleDSM]

If by hesitation you mean a misfire then no, I'd say that non of those options will be the cause. If you mean that the car just feels like it lacks power than I'd say that the lack of knock sensor is throwing the ecu into safe mode pulling timing. You need a knock sensor in there.

The bad ISC won't cause a lack of power or misfire or hesitation. Just idle issues.

 

[shrewmouse]

If by hesitation you mean a misfire then no, I'd say that non of those options will be the cause.

Right, misfiring is what I mean. It's not running smooth at all when it reaches 4.5K RPM. If I switch into a lower gear I can continue to accelerate smoothly until I get into the 4.5K RPM range again. 4.5 K is pretty consistent but not exclusive. Sometimes more; sometimes less.

If you mean that the car just feels like it lacks power than I'd say that the lack of knock sensor is throwing the ecu into safe mode pulling timing. You need a knock sensor in there.

So input from the knock sensor causes the ECU to retard accelleration but not cut off fuel?

The bad ISC won't cause a lack of power or misfire or hesitation. Just idle issues.

Could the bad ISC "confuse" the ECU? Perhaps resetting the thing would help fix the problem? I'm shooting in the dark here.

Thanks for everyone's help. I'm thinking that I shold video tape what's happening so that everyone knows exactly what I'm talking about.

Thanks again

 

[5150DSM]

Right, misfiring is what I mean. It's not running smooth at all when it reaches 4.5K RPM. If I switch into a lower gear I can continue to accelerate smoothly until I get into the 4.5K RPM range again. 4.5 K is pretty consistent but not exclusive. Sometimes more; sometimes less.



So input from the knock sensor causes the ECU to retard accelleration but not cut off fuel?




Could the bad ISC "confuse" the ECU? Perhaps resetting the thing would help fix the problem? I'm shooting in the dark here.

Thanks for everyone's help. I'm thinking that I shold video tape what's happening so that everyone knows exactly what I'm talking about.

Thanks again

First thing you need to do is find out for sure what engine and ECU are in your car. Look for the VIN stamp on the engine block and match that up to the corresponding make/model. Next, is the car throwing a code or not, your first post is contradictive and the answer makes a difference. The ISC issue is simple... replace the throttle body. The misfire/hesitation issue is more than likely related to your lack of knock sensor(which is quite neccessary in our cars) but we need to be sure of the engine/ECU configuration before the answers are clear. BTW- Are you sure there isn't a knock sensor, have you personally verified this? They can be somewhat hard to find the first time around.
Aloha

 

[thebird_19]

I had that problem before. It turned out to be leaking compacitors in my ecu. Don't know if yours have been changed, but mine leaked on some chips which caused the fuel pump relay to turn on and off. I've read that is a common problem. I changed my compacitors, but the damage was already done and the ecu went out a week later. Now I have an awd ecu from the same year and my car runs fine.

 

[shrewmouse]

The problem has been solved. First of all thank you to everyone that tried to help. I appreciate it.

My new mechanic got to the back of the engine and found the knock sensor. He hooked it back up and bingo! Now the car doesn't hesitate/sputter at 4.5 K.

My error was trusting my old mechanic.

To recap, I have the correct engine, the knock sensor was replaced, the ISC was not replaced.

Thanks again!