Is this normal Idle

fitz · fitz's Garage

I have an 88 cab and since I purchased the car a year ago the car seems to idle like a Harley Davidson. Is this normal? The car runs at a consistent idle but the car shakes especially when standing still. The car seems to pick up fine, but the idle concerns me a little. I read all the previous post on this topic and based on the suggestions I changed my plugs, cap, rotor, and air filter and thought that would give me a smooth idle. However, the ideal is still rough. Please any suggestions would be appreciated. Also, one of the post I saw mentioned changing the DME, does anybody have a picture of what this looks like?

Thanks again any replies.

Ron Fitz

cowtown · 08-14-2003, 07:57 AM

Definitely not normal. The car will run on 5 cylinders. Have you checked for spark at all cylinders? After that you could check each injector. Might want to run a compression test too.

If it's running and never cuts out intermittently, it's probably not the DME or DME relay (which is also the fuel pump relay).

1fastredsc · 08-14-2003, 08:16 AM

What's the idle value, anything at like 800 or so will start shaking up the idle. I could also not be running on all cylinders as stated by cow.

fitz · fitz's Garage

Colin,
Thanks for the reply. When you mean check the spark at each cylinder, do you mean pull the spark plug cable and see what happens? If this is correct, what should I be looking for? Also, just to add to my dumb questions, would it be wise to add a fuel injector cleaner/additive to see if it will clean out the injectors. If so, any recommendations? This morning the thing idled great but usually when its sitting in traffic it starts to rock the car a little. The idle is at a consistent 800 to 900rpms every time and does not cut off at all.

Oh, also I had a valve adjustment done about 600 miles ago, so I know it can't be that

Any ways, thanks for the help?Fitz

ZCAT3 · 08-14-2003, 11:31 AM

Fitz - that sounds similar to what my 87 did. It idled right around 800 and had a little shake to it. I replaced the O2 sensor (which is supposed to be done every 60,000 miles but almost no one does it as routine maintenance) and cleaned out the idle stabilizer valve. That did it - the idle smoothed out nicely.

RickC · 08-14-2003, 11:44 AM

Replaced everything $$$ and couldn't get the shake out at idle (though everything I tried did improve things a bit). Finally took it to a wrench to set the CO, which I saw was low during a smog check. When set to normal it started severely misfiring.

Seems that though I tightened the intake manifold gaskets to spec (18lbs if I recall), they were cracked and leaking air causing a misfire. Replaced them and set the CO and now it idles perfectly.

Bad idle started suddenly one cold day, so I knew it was something. When I started talking the plasticity and pliability of cold/hot materials, this really well respected wrench just sighed and said "the gaskets are just old."

Obviously he was right. They can't be expected to keep a perfect seal forever. Do the simple, easy to eliminate things first. Get some $3 carb cleaner and spray it at the base of the manifolds to see if you have a leak. Seals are like $50 and easy to do.

cowtown · 08-14-2003, 12:29 PM

fitz,
With the added information that it sometimes idles ok and sometimes does not, I'd have to agree with ZCAT and RickC...I thought from the original message that this was a constant problem. You most likely do have good spark and fuel if it's just an intermittant thing.

It never hurts to run a bottle of Techron through the system. Don't expect it to solve this problem, but it's a good idea anyway.

Good Luck!

Bones · Bones's Garage

Damn you guys are always mentioning Techron , we don't have it here , (at least I haven't seen any ) . Is it like Red-X injector cleaner . I assume you have Red-X ?

fitz · fitz's Garage

You guys are great! Have you all thought about going in to Porsche Therapy counseling. You give advice that can be very helpful unlike regular therapist that charge you $80 an hour and just smile at you and tell you to get in touch with your feelings.

Anyways, Zcat thanks for the advice, if Wayne has O2 sensors I'll order one tomorrow. As far as I know, the PO didn't replace this at all and there is about 107,000 miles on the engine. I think it's about time the O2 sensor got changed.

Another dumb question, what and where is the idle stablizer valve?

RickC thanks for the reply, after I try Zcat's advice and the car still idles rough I try you suggestion next.

Colin thanks again for the information. I thought when techron was mentioned on the board I thought they were talking about Chevron gasoline with techron. So, I've been filling my tank up for the last few months just with Chevron gas. (No, I'm not a blonde, but I am getting a lot of grey in my hair). Now that I know what you guys are talking about I go buy a bottle. Thanks again Colin

Bones, once I find a place to get Techron, I can pick up a few bottles for you and mail them to you if you want. Just go to my profile and email me your info if you want me to ship you some.

Thank again for the advice....Fitz