I Took Out My 1991 C4 Coupe, 7400 Miles, After Not Using For Several Months. After The Engine Gets Warm The Engine Begins To Idle Very Roughly And The Car Makes A Loud, Very Loud, Knocking Noise. Can Anybody Point Me In The Right Direction?

 

sell it to me

 

We need lots more information. Does the knock coincide with engine speed? Are all gauges reading where they should? Does the knock occur when you are stopped? When in park and neutral? Did you check all fluid levels? How long did it sit? How old is the gas? Did you open the hood and listen to the noise? Try to locate the sound by listening through a hose? Does it happen with climate control system off?


I'm probably forgetting some, but those answers will help?

 

Thanks alot, I really love the car and I am quite concerned.

 

make me an offer I can't refuse.

 

I had the same knock you described. After many efforts to solve it ( replacing injectors, playing with timing, wires, plugs) It statred again and I got so PO'd I pushed the TPS lever all the way down and loaded up the engine, it started running super bad, missing and it finally stalled, the check engine light came on also. I replaced the the TPS with a GM oem and it hasn't done it since. Now, some people will chime in and say it has nothing to do with the TPS, but I only know I can replicate the knock if I hold the TPS down. I hope I never that knock again, It sounds like the crank is about to come thru the oil pan.

 

Sorry for my lack of knowledge, but what is a TPS?
:o

 

Throttle Position Sensor

 

It does indeed sound like the crank is going to go through the pan. Before I go ahead and replace the TPS do you know if there is a way I can test for this?

 

Does it really run well when cold -- a OK? Is it quiet (smooth) before the engine is warm or just quieter (smoother)? If quiet when cold and if it idles well when cold, then the onset is associated with going into closed-loop control (computer regulated fuel and timing based on input from sensors, including throttle position, O2, air temp, MAP, etc.). It would seem that the ECM probably has bad information.

The noise might not be very important except that it is caused by a poorly running engine. That said, for isolating noise, there is a great device called a mechanics stethoscope. It costs about 15 dollars and looks like something that you might see at the doctors except that it has a rod at the end of the tube. I recommend that you buy one. The rod transmits sound remarkably well and you can also pull of the diaphram and rod to use the tube by itself. You can stick one end of a 1/2 inch tube in your ear and move the other about, but it isn't the same quality. Your local Sears should have one as should some autoparts stores.

You should be able to narrow down the source of the noise pretty quickly but it is beginning to sound like the engine is just running so badly that your putting weird stress on the driveline -- running on a few cylinders and fuel igniting at the wrong time.

These are my best ideas but there are much better mechanics than me on the list. If the car runs OK which cold, I would try to hook your computer to a scanner to determine which sensors are wacky and that might mean a trip to the mechanic.

 

Lets say you had an injector goign bad and had a mis....If you have a 6 speed, dual mas flywheel the miss can cause the noise to come from the flywheel (knocking) yet have you thinking its the bottom end.

First thing is to get it running smoothly...Bet the "knock" goes away.

 

Check your plug wires .Sounds like two of your cylinders are cross firing .

 

Are you suggesting to check if the plug wires are in the proper order, or to replace them? The 1991 is completely original, including its 16 year old plugs and wires. I have never had any rough rides in its 7400 mile lifetime until now.

 

THANKS CHATMAN.

FROM WHAT I'VE BEEN READING I AM STARTING TO THINK THAT THE ROUGH ENGINE IS CAUSING THE FLYWHEEL TO KNOCK AND MAKE THAT AWFUL NOISE. THAT SENDS ME BACK TO THE ROUGH RUNNING ENGINE.

I AM SURE THE ENGINE PURRS WHEN COLD. DO YOU KNOW IF I GET THE MECHANIC TO CONNECT TO THE COMPUTER WHEN IDLING ROUGH, WILL HE GET THE INFORMATION HE NEEDS?

 

SOUNDS LIKE A LOGICAL PLAN.

 

Howie,

Have the mechanic ohm the injectors, I will bet one or more of the are bad.

Good luck

Randy

 

thanks will do.

 

I went ahead and changed the TPS and it did not do the trick. The car runs great when cold and powerful on the parkway. But when warm it wants to stall, had to keep the engine revving above 2000 to get rolling in first. Finally the engine does stall, and will not start unitl absolutely cooled off.

HELP!!

This is a terrible way for a Polo Green and tan 91 with 7500 miles to behave.

 

Have you checked the injectors ? They are easy to check. I think they should be no less than 16 ohms. My knock started when I ran Seafoam cleaner thru my Multec injectors and killed them. When they got hot it would knock loud. Cool they ran fine. After replacing them and getting the TPS and other componnets right it finally runs right. My comment of loading it up with the TPS kinda proved to me it has more to do with a poorly running engine other than an failing internal part. Hope you figure it out.

 

I will check the injectors and get back to you.

thanks.