rough idle

[monterey1962]

Had the '88 out today to run to the store and noticed her idle is getting pretty rough. Damn near wanted to die out. I've been noticing that her idle is worsening since I brought her out of storage. I believe I've replaced all necessary maintenance parts in the past two weeks.

Tomorrow I'm going to pick up a new IAC valve and try that.

Any suggestions as to what else it could be?

-------------------
Justin

[NATEHAWK]

Try that seafoam and check all ur injectors for proper connections.. make sure nothing is loose.

[marquisman]

you ever check the PVC and filter on the back of the intake?

[zwack88]

When was the last time you gave her a good ol' fashon tune up? Ya seafoam that bish and replace the PCV and fuel filter if it is due.

[monterey1962]

She just got a FULL tuneup in the last two weeks. My girl is getting royal treatment since the truck is gone. I put a list of most of the things I've changed at the end of my "Project Super Unknown" thread a while back.

I just finished cleaning the throttle body. It was pretty dirty. Didn't take the IAC valve off, but drown the hell out of it with cleaner. Ran her for about 15 minutes without any trouble. Guess all it needed was a good cleaning. If the problem comes back I'll get a new IAC valve.

------------------------
Justin

[trwp72]

Throttle body butterfly valve....

It is amazing what a good cleaning to the butterfly valve in the throttle body will do... most of the time problems like you described.. the best thing to do FIRST is to clean that area up... just a little coating of junk on it will make your car run like crap.. First time it did it to my '88 I had, my mechanic told me how to clean it.. I thought he was nuts!!! (I had adjusted the idle adjustment screw WAY up to get it to stay running...) I took it up to the firehouse, cleaned it up... fired it up.. and the idle went to like 2000 RPMS.... had to back the idle screw back down to the original setting... amazing the difference!

[gadget73]

Most of the time you don't need to replace the IAC. A good cleaning often fixes it up. Just take it off and spray the hell out of it. I did that with mine and it smoothed out nicely.

[monterey1962]

I didn't mention that the idle was rough only when the engine was warm. Was rough again today and I picked up a new IAC valve, but I had to run her to the shop. Heater core troubles along with a few other things on the list. Too busy to mess with it myself.

-----------------------
Justin

[zwack88]

I just got done cleaning the T.B. with some T.B. cleaner. I did it cause my car just got new plugs and fuel filter and it ran fine but today under slight throttle she was like back firing alittle cause I heard the exhaust popping and it never did that. So after school I went to Advance auto parts and got a can of throttle body cleaner and a new PCV valve cause I never replaced it and I didn't know when the last time was it was replaced. So I took my zip tube off and looked into my T.B. and that thing was really sick looking. I had about 20 paper towels covered in black shit. Then poped the new PCV valve in and now she runs like a dream. By the way that old PCV valve was the original one. I though P.D.s did all this routine maintance and so far all I can see that was changed was the oil and the air filter. Now she has way more performance and I think my car has way more balls than it did the day I did it. I should have taken before and after pics of that T.B. it was amazing it came so clean and it was that dirty.
Hopefully my MPGs go up cause with the new plugs in and fuel filter I was only getting 12 MPG in town. I think it will go up considerably.

[monterey1962]

The rough idle is still there from time to time.

One thing I've noticed is that the engine bogs down when the heater is turned on. There is a noticeable pull on the engine when the blower speed is turned to "high". If I get on the gas a bit then let off, it seems to idle better again.

What are the signs that an alternator is going bad?

---------------
Justin

[Grand Marquis GT]

This may be a sign that the thing that kicksw your idle up when the A/C compressor kicks on isnt working...

At least thats my guess.

[monterey1962]

Well, even after Sea Foaming the car, she still has the occasional rough idle.

Could a clogged PCV screen cause this? It has a new PCV valve. I've sprayed around for vac leaks and haven't found anything yet.

Which way does the vaccuum travel through the PCV valve; up out of the lower intake, or down into the lower intake?

------------------------
Justin

[85crownHPP]

it pulls vacuum into the intake.
it could be the cause, especially if you dont think its been changed recently, or at all.

[monterey1962]

Is there a trick to get that screen out? Special tool needed?

----------------
Justin

[gadget73]

long drywall screw and a pair of pliers. Thread the screw into the screen and pull it out. Drywall or wood screws should do fine for this. Might be able to get it out with a pair of needle nose pliers or dental picks, but the screw method, while not being very fancy, works out ok. Might as well replace that rubber grommet for the pcv valve while you're in there.

Also, if you suspect charging system issues, stick a volt meter on the battery and see what you get. With all the stuff running (lights, blowers, etc) you should still see better than 13 v at idle, ideally closer to 14v. Could be a poor ground or battery connection causing this too, if the voltage drops too much the ignition system will be weak and I imagine the PCM will get funky as well. Check/clean all your connections on the battery and starter relay as well as the ground connections if possible. There should be one on the passenger's side attached to the rear of the head, and the ground cable runs to someplace right above the airpump on the block. I think Autozone will load check alternators for you as well, so that might not be a bad idea to look into.