I just picked up a 2002 VDP that was sitting for a couple years (71k miles). After replacing the fuel pump (what fun! ) the engine fired right up.

The issue is,,,,,,,, when the engine is cold it has a knock, but only at idle. If I increase the rpms even slightly the knock goes away and once the engine comes to temp the knock is gone completely. The knock is loudest at the rear of the engine and when occurring can definitely be "felt" when placing your hand say on the throttle-body intake tube. If I had to guess I'd say the knock is coming from just under the intake area and does not appear to be a bottom-end knock.

I was told by the previous owner that the guides/tensioners/etc. were replaced at ~52k miles.

I know that's not a lot of info on which to go, but any ideas what this might be? I would like to troubleshoot, but don't really know where to start. Other than the "temporary" knock, the engine runs great.

Thanks,
Dan

 

Use something like a long screwdriver to your ear and see if you can listen to certain areas to isolate the noise.

 

+1. At your closest auto parts store, buy a mechanics stethoscope. Put the probe on the throttle body and work forward. May need to do this over a few days if the knocking/tapping quiets as it warms up.

Given it has been idle for a while, maybe sticking fuel injectors . . . ? Put the probe on both the right and left rails.

Nice town, Delaware: my youngest flunked out of Ohio Wesleyan once (and twice from Ohio State).

 

Mine makes a noise that also only happens at cold idle. I went through all the obvious steps to try and troubleshoot it :

Checked with mechanics stethoscope.
Checked compressions.
Checked for play in the big end bearings.
Tried driving with the supercharger belt off to see if is related to that.
Checked valve clearances.
Checked chain tensioners.

All I can tell with the stethoscope is that it comes from the upper half of the left side of the engine.

Here is one important suggestion : determining the frequency is important to diagnosis.

A crankshaft issue should be at crankshaft frequency.
A rod knock should be at crankshaft, or x2.
Valve issues are at half crankshaft frequency, once per 2 rpm.

My noise sounds like a valve issue. As the engine is as quiet as a church mouse when warmed up for even just a few minutes, I have decided not to worry.

I believe that, because the engine is otherwise so quiet, any noise is very obvious. This noise would be totally inaudible on my TR8.

The noise has not got worse over 3K miles. A rod knock would get worse rapidly.

 

I'll break out the mechanics stethoscope (already have one) and see if I can track down the exact location.

Delaware: Nice town, yes, except those months when the white death falls from the sky. We live about 1.5 miles from OWU.

This knock sounds like someone tapping on a large clay pot with a 2# hammer (i.e. deep/hollow sound). It reminds me of a spun main bearing knock in a small-block Chevrolet, but that doesn't just go away. The harmonics are either crankshaft frequency or the frequency of the same piston firing over and over.

If it were a rod/main bearing knock I would expect the sound to get worse and eventually for the engine to get 'tight', but it's just the opposite. Once warm it's super quiet and turns over easily.

Hopefully the stethoscope will point me in one direction or another.

Thanks,
Dan