'86 245 DL w/fast idle

adjunct · Post by **adjunct** » 11 Mar 2007, 18:06

The original alternator in this car died last week while I was on the road (at >186k miles, I think it had its day), so I had a local (not my regular) mechanic replace it. On getting it back, I noticed it has an extremely high idle- I don't have a tachometer (never bothered to replace the OEM analog clock with a tach), but it sounds like it's 'idling' at around 4k-5k rpm, high enough that I nearly overheated while sitting at a long light earlier today.

The obvious suspect is incorrect tension in the belt assemblage, but after working with the adjusting and pivot bolts for the alternator this evening, I had no luck with either more nor less tension, even after cranking it down pretty far. Is there something I'm missing here, or do I need to look at the other belts as well?

Post by **billofdurham** » 12 Mar 2007, 13:16

I don't see how the drive belt tension would affect the idle speed. The simple check for correct tension is to press firmly on the centre of the longest belt run and the belt should deflect by up to .5 of an inch.

It is much more likely that the mechnic has disturbed something whilst working on the alternator. How far away is he? If it were my car I would be taking it back.

Bill.

adrianpike · Post by **adrianpike** » 12 Mar 2007, 15:27

4-5k rpm is basically redline, assuming an M cam. If it's actually as high as you claim, I'd be on the hunt for a post-TB vacuum leak the size of Texas. A spray bottle filled can help find the leak, spray lightly until you notice a stumble.

Also, the fact that it's overheating at a light is indicative of something else wrong. Check base ignition timing, and check the fan clutch.

Drive belts are not your problem.
I might have a tach that you can have for shipping cost, if you'd like.

adjunct · Post by **adjunct** » 17 Mar 2007, 17:49

Thanks for the suggestions. Too cold to work on it this week- I'm in central New York, no heated garage- so I left it with the mechanic who'd done the work, since I was passing through that town again. Apparently, he'd left a vacuum hose disconnected- didn't think he'd need to disconnect any for an alternator replacement, but I'm satisfied either way.

Adrian, I'll take you up on the tach- sending a PM.