Poor Idle on '89 3.2
 

I've got an '89 with pretty low miles (19k), and have had it for about a year. It drives and idles fine during warm up, after I drive for a half an hour or so, and I pull up to a street light - it settles at a smooth 800rpm idle at first....

But if the light is long, more than a couple a minutes, it starts to sputter and the idle gets very poor - between 500-700 rpm. It never stalls, but sputters. If I give it a littel gas, it settles out, but then returns immediaely to the sputter if the gas is removed. Drive fine, and when I pull up to the next light same thing, first ok, then sputter.

Any ideas on were to start looking?

The plugs are less than a year old, installed by the P.O., I don't think the wires, rotor or diz cap have ever been replaced.

Keith

I'd start with checking hoses/fittings look for loose or cracked lines/fittings. Even with low miles the rubber/plastic can deterioate.

If you don't already own it, buy 101 Projects and check/reset idle.

After that, I'd suspect the Oxygen sensor. IMO

Keith2

Keith, you might want to torque down your intake manifolds, or at least, check to see if some of the nuts got loose.

Cheers,

Joe

I would suggest removing and cleaning the air idle bypass (pod on throttle body with 2 hoses connecting to it). I found mine was causing very poor idling an after cleaning all is well. Use carb or brake cleaner.

Check for vacuum leaks (cracked or loose hoses) and you might as well change the distributor cap and rotor arm if they're the originals.

All great suggestions. I'll look into them this afternoon and see if it helps. Thanks everyone.

Keith

head temp sensor.....easy fix.

Spray some carb cleaner around in the engine bay when idling to see if there's an air leak somewhere. It is the cheapest problem you could fix, so start there first. Otherwise you'll adjust the valves, get a new 02 sensor, new cap & rotor, and new 2 wire CHT sensor (really hard to get at) and still have the problem - ask me how I know.

My 87 Targa has 29000 miles on it and had a similar and annoying idle problem. Would idle at 880 for 30 seconds and then drop and be rough. Tried everything, noticed it felt rough too, and turned out #1 cylinder was missing at idle due to an intake manifold gasket leak (gasket was ripped and twisted out). The problem started suddenly one cold day last November.

Gaskets are cheap, but you need to take apart a good amount of stuff to get to them (I took off heater, A/C, Air Meter and disconnected the fuel lines to the fuel rails to raise up the manifolds enough to get the new gaskets & spacers on). Not hard, just time consuming. Now the car runs perfectly like it did when I bought it.

My idle problem is a little diffeerent. Once it's warm, it settles at about 1000 RPM and runs like it's missing. It kinda has that big cam sound, but less rhythmic. Once the revs are up, it runs fine.

I checked all the stuff the Bentley book says to check with good results. The CHT sensor is less that 10K miles old, as is the O2 sensor. I can't find any bad or disconnected vacuum hoses and all the intake bolts are tight.

I haven't tried a valve adjustment. I suppose I can try that before taking the intake stuff apart to replace gaskets.

Any other ideas?

My car ran fine off idle too. And it may not be the manifold gaskets, but please set my mind at ease by trying the carb cleaner. The first thing I did after consulting this site was to tighten the manifold bolts. They were about tight enough, and gettting them to spec made no difference. So I thought "well, of course that was too easy, and the car doesn't have many miles so that wasn't it" and then spent the rest of the summer chasing phantoms. All because I assumed that wasn't it and therefore didn't spend the $3 that would have shown me the way....

It drove me nearly crazy, and ruined my enjoyment of the car for the whole summer. If the carb cleaner helps you, maybe a little of that lost time and frustration will be redeemed......
If not, you'll be able to fully eliminate a vacuumn leak......