Ive searched and searched the site and haven't found a post that says a fix so Im asking before I dump around $500 on everything I can think of. The truck (88 SR5 turbo 22rte 127k miles) has a bit of noise(light metallic sound) at idle with an erratic bump to the rpm. By bump I mean a distinctive drop of 50-100 rpm with a slight misfire. At speed the engine runs great. No problems from a stop or getting up to power. My only two things I would guess are ignition part or timing chain. I've put a timing light on it but seems like the timing mark bounces around a lot. My vac gauge reads a bouncy 16-17 inches of vacuum with the bounce sticking around 2 inches difference and going down not up. Things I just did were replaced the cyl head new turbo and cyl head gasket. Comp was 126-127 all four cyl. Leak down check had no signs of gurgling or loss of pressure. No water in the oil. No oil in the water or bubbling. Any ideas?

 

I vote for bad distributor. My girlfriend said "it sounds like my car is grinding up aluminum cans." Her description was spot on; it was the distributor.

So find the sound first. You can spring for a fancy stethoscope http://www.harborfreight.com/mechani...ope-69913.html , but I've found the tube inside a roll of paper towels works just fine.

 

Or a big screw driver will work too. Have you pulled the distributor and checked the gear for abnormal wear? Excessive shaft play? As Scope said, you need to find the cause of the grinding noise first.

 

I used my cheapo Oreilly stethoscope and found the clicking noise was louder right below the plug for the valve cover where the cam bolt is. I also heard a slight ting where the chain guides were but not sure if its normal or not. Might have been the chain moving across the guides.

I had the distributor out when I pulled the cylinder head out and from what I could see it was normal. I didn't check it for side play however. Ordered up a new dizzy hoping that's what was wrong because of the clicking but if Im wrong I have to do the chain which Im really hopeful it wasnt because I just had the front of the motor apart a week ago.