Hi all. I bought this car about 6 months ago and have been slowly working on it. It drives fine, but idles rough and has extremely high emissions. I've done quite a bit of reading and It idles about 1800 on cold start and idles about 1200 when warm. I've replaced the coolant temp sensor, oxygen sensor, and done plugs and wires, oil change, and fresh gas. There is no check engine light on.

I think the MAP is working fine. Pulling the vaccuum line causes it to immediately drop idle until the point it almost dies. Pulling the MAP sensor wire also makes it almost die and lights up the check engine light. I read a post about checking MAP sensor voltage at the blue wire, but my wires are grey, green and black with red stripe.

I assume there are no stored codes because the check enging light is not on. Correct me if it is possible to have codes stored with no light and I will go check them.

I can't get this car registered until it passes emissions. Besides I want the car running correctly. Any help would be great.

Here's a video of the rough idle at the tailpipe: http://www.youtube.com/watch?v=Lea_ktWaUDM

Fieros are supposed to retain stored codes. I have read about exceptions, but usually they stay in the computer after the light has gone off.

[This message has been edited by Gall757 (edited 01-27-2013).]

OK, I'll check codes, although I suspect I have polluted the codes with a bad MAP sensor code because I pulled the wire while running. I am guessing I need to pull the battery wire to clear all codes?

I also need to check the injector to make sure it is producing a nice stream according to other posts I've read.

Any other possible things to look at?

High idle on warm/hot engine likely mean vacuum leak.

See my Cave, Vac Leaks

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

Thanks, ogre. Your sage input is appreciated. I had not seen your vacuum leak page. I will go forward with vacuum leak as the next most likely cause.

UPDATE: It was a bad EGR valve

Following Ogre's info on diagnosing vacuum leaks, I started poking around the vacuum lines. I noticed that the idle did not change when I pulled the vac line off the EGR. I found this awesome video on testing the EGR valve. After pulling the EGR valve off my engine, I discovered that mine had exactly the same behavior as shown in the video, with no vacuum being retained when plugging the hole for the vacuum line and depressing the plunger. New EGR ordered and should be here tomorrow.

Also, the EGR port on the intake is really crusted up with carbon. Reading other posts here, it seems like best bet is to just leave it be until a future time when I can pull the whole intake and give it a proper grinding out/cleaning.

I am posting this info in the hopes that it might some other newbie in the future who might have a similar problem.

Still having issues. Idle still stutters and cannot pass emissions test due to high hydrocarbons (unburned fuel). Still sounds much like the original video posted above with the intermittent "dug dug" misfire. I suspect Ogre is right, vacuum leak somewhere causing a lean misfire due to unmetered air entering the system.

I've owned this car one year and despite my money and efforts, cannot get it legally on the road due to this problem. I am almost ready to permanently walk away. I know my wife would be happy if I did.

Since January when I first posted this topic, I've had the head professionally rebuilt (coolant in oil) and I put the whole top end put back together including a new EGR valve, as mentioned above. I've also followed the Ogre's cave advice on diagnosing vacuum leaks. I plugged the canister lines and the brake booster line at the intake and there was no change to the condition. There is no cruise control installed, so that is not a factor. Next I hunted around with throttle body cleaner but cannot get the idle to be affected by the spray at any point.

I have not tried replacing MAP or MAT but symptoms all point to vacuum leak, so I don't want to throw money at the problem.

I may have a lousy ground too. The ground block on the belt side of the cylinder head is currently grounded to the right strut tower nut. I know this is incorrect but I don't know the proper grounding location. I should have taken more pictures before I pulled the top end apart.

I even went so far as to take it to a local shop this week and tell them I think it had a vac leak. They came back and said I needed a new catylitic converter. Worthless.

Not sure where to turn next. Thoughts anyone?

I am thinking that high hyrdrocarbins is not a lean problem, it is a rich problem? Larry

quote Originally posted by CaravanBill: They came back and said I needed a new catylitic converter. Worthless.

Don't be so quick to rule that out as "worthless".

My experience with dukes ('84 and '87) is that they will not pass smog tests without a properly functioning cat.

What makes you so convinced that your cat is fine?

quote Originally posted by Patrick: What makes you so convinced that your cat is fine?

Being 25 years old it probably could use a cat, but I'd like to get it running properly and see if that solves the problems before dropping cash on a cat. Could a clogged cat cause idle/sputtering issues?

quote Originally posted by CaravanBill: Being 25 years old it probably could use a cat...

Oh good gawd... you mean to say it still has the original cat??!!!

Good luck with ever trying to pass a smog test with that!

quote Originally posted by CaravanBill: ... I'd like to get it running properly and see if that solves the problems before dropping cash on a cat.

Might be slightly different requirements in different jurisdictions, but my experience is that even a perfectly running '84 and/or '87 duke will not pass smog testing without a good cat. Dukes are dirty engines. And 88's have to meet even stiffer smog restrictions here than the earlier years. Might be the same where you are.

quote Originally posted by CaravanBill: Could a clogged cat cause idle/sputtering issues?

My only experience with a clogged cat was with an '86 GT. It seemed to idle okay, but would not rev much beyond 2500 RPM.

quote Originally posted by Patrick: Oh good gawd... you mean to say it still has the original cat??!!!

I don't know how I would know how old the cat is. Is there really any way to tell how old a cat is?

It doesn't have any trouble accelerating. It get's up and goes pretty good actually (for a duke).

Has plug over the idle stop screw is off?
If PO mess w/ idle stop... reset it w/ info in cave.

Missing then check ignition.
Missing will cause high emissions.
Iffy coil(s), plug wire(s), plug(s) etc. can cause missing.

See my Cave, Idle Stop and DIS Ignition

Old Cat can pass... My car has OE cat and pass every two years. In this spring it passed again.
But Many things can kill the cat... running a year or more w/ missing problem and high idea is not good.

To tell OE unit... first just look. New cat's are small and need a pipe to reach the ends of OE exhaust. OE cat is much bigger.

[This message has been edited by theogre (edited 08-11-2013).]