I've noticed quite a few threads involving the 2.5 and intermittant stumble, missfire, etc. I was chasing this problem for over a year. Just off idle there was a stumble that went away once you applied a little more power. Occationally the check engine light would come and go, showing a rich condition. Most times the car would run great but this just kept things from being perfect. I went though coolant temperature sensors, TPS sensors, MAP.... you name it. I swapped out good know parts and everything seemed up to spec. The same for the distributer componants and the plugs/wires. Colder weather seemed to make the sputtering worse when it was acting up. Sometimes you would be driving down the road at highway speed and everything is perfect. Then a few sputters and a check engine light. All of a sudden it clears out and runs fine. Sound familiar?

EGR. Even though the valve was functioning, it appears that for some reason this engine doesn't like it. I finally just pulled the vacuum line and plugged it. The off idle stumble is gone. The intermittant check engine light is gone. No occational stumble at speed either. I'm going to do some further testing and research in to exactly why this is going on, but I thought I would share what I've discovered as it appears to be a common symptom. See if this makes any difference on yours. Mine is engine is more responsive and peppy (if you can say that for a 2.5) and is now a pleasure to drive.

i know the problem all 2 well... any pictures of what you did... i am having trouble putting it together in my head

just checking.. you swapped the o2 sensor? Check your plugs, coil, battery cables, ground? Just thinking as I haven't had this problem with a 2.5L. Also, have you checked the injector incase it is dumping too much fuel?

Just thinking aloud.

J.

Yes, 02 sensor is new. Fuel injector is new. ECM is new. This car has documentation since new of every repair, including a new long block at 136K. Since I have a scanner I was able to verify the condition of every sensor, once everything was as new and the stumble was still there is the point that my search to cure the intermittant miss began. Extra grounds were added, even the fuel pressure was verified. Merely unhooking the vacuum line to the EGR and plugging it so there was no vacuum leak cured the problem... esentially bypassing the EGR completely.

Somehow the introduction of exhaust gas is causing the problem. Perhaps improper metering, introduction at the wrong time, or it just plain doesn't like it........ not sure yet. Since the engine doesn't like running while my scanner is in operation it will take some additional time to figure out what is going on.

I believe the ECM needs to re-learn the air/fuel ratio and spark advance to account for the new EGR valve.

I had the same stumble/hesitation ptoblem when I replaced the EGR valve on my '87 Duke. Clearing the ECM memory and driving the car for a bit solved the problem for me.

I don't know if this can cause what you said but--I have found the intake to the TBI from the EGR ploged with carbon. Removing the TBI and gasket will; uncover the carbon tracking.

Here are a few pics for those in need.

the first pic you see the traditional 84 2.5 engine bay.

The next pic is a close up view of the general location of the EGR as it sits below the air cleaner assembly. In the bottom and the bottom right corner you can see the hose to the PCV valve, the upper left is the air cleaner assembly.

The last pic shows the air cleaner removed for easy access to the EGR valve. In the photo you can see a shortened golf tee that I used to plug the hose end that was pulled off the EGR valve.

Believe me when I tell you I went over everything. My scanner was doing overtime on this car! Resetting the computer had no effect and it's part of my regular diagnostic proceedure. For some reson, this engine just didn't like EGR. I'm still going to open things up and see if I can ultimately get EGR to function correctly, but at least I know that if I cannot, the bypass fixes the drivability issue. Hope this info helps.

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Competition Yellow 84 2.5 Bone stock right down to electrical gremlins

[This message has been edited by Joe 1320 (edited 02-09-2006).]

The only problem is that without the egr you will have to run premium gas. I know for a fact that it will ping like crazy and that is hard on the engine.
I have noticed some minor problems with the egr on my daughter's 2.5 also. The thing has an intermittent miss when not under a load that disappears when the egr is disconnected. Out on the road with everything hooked up the car pulls good, cruises good and gets 29 mpg in combined driving. It does have a hestitation/stumble when it's cold, but that goes away within a minute after it's started. The cold hesitation has been in all the dukes I've ever driven (and that's several).

Dave

By the way what aldl interface/software are you using. Just would like to know in case I get a L4 some day.

I had a very eratic stumble in my 85 and it all cleared up with new plug wires. It's always breathed well and has lot's of power, but is very sensitive to cold and to moisture. Make sure, if it's cold outside, you let her sit and idle until the RPM's drop before you drive it. If you just hop in and go, while it's very cold, I've seen it confuse the computer and they drive like heck (stumbling and such). This stands true with both my 84 and 85, but I have to say the 84 is worse.

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Jay Brintnell
White 85 Notchback(A.K.A. GodFearN)
Red 85 Notchback (work in progress)

quote Originally posted by Eclipse: I had a very eratic stumble in my 85 and it all cleared up with new plug wires. It's always breathed well and has lot's of power, but is very sensitive to cold and to moisture. Make sure, if it's cold outside, you let her sit and idle until the RPM's drop before you drive it. If you just hop in and go, while it's very cold, I've seen it confuse the computer and they drive like heck (stumbling and such). This stands true with both my 84 and 85, but I have to say the 84 is worse.

The EGR bypass solved this on mine as well. It really makes me wonder about changing the metering of the EGR. It should be tuned to not cause drivability problems. If after testing the EGR vavle itself as well as checking all the passages for excess carbon, etc. everything is as designed, I will experiment with regulating the EGR. EGR is beneficial, but incorrect metering can make an engine run really crappy.

[This message has been edited by Joe 1320 (edited 02-10-2006).]

Great info here. My Indy has the slight bucking, when at part throttle, or when letting off slightly. Pulls good, other wise. I just haven't taken the time to fully investigate. Was waiting for warmer weather, but might check into this. Thanks guys.

Kevin

As part of my diagnostic, I drove it to work today with the EGR functioning. Every so often the engine would stumble with the accompanying Check Engine light. In the 10 mile one way commute the stumble and light occurred perhaps a half dozen times at least. As soon as more power is applied the engine cleans up, the Check engine light goes out as per previous tests.

Definately an EGR metering issue.

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Competition Yellow 84 2.5 Bone stock right down to electrical gremlins

[This message has been edited by Joe 1320 (edited 02-10-2006).]

the egr was causing the same prob on my 88. I put on a used egr that i had and it runs just fine. No more stumble. JM

TTT

Another place to check for a problem with the EGR system is the passage channels under the throttle body. I was working on the classic hunting idle on my 84 when I removed the throttle body to clean it and replace the gasket. When I removed the gasket I found the passages under it were completely plugged with carbon, so even though my EGR system appeared good the gasses had no where to go when the valve opened.

Hello,

I have an 86 2.5L and I also experienced the same problem with the intermitten bucking/surging and after disconnecting the EGR and plugging the TBI port that resolved my problem too. I recently took a look at the problem again and after not finding any vacuum leaks and replacing all the vac lines to the TBI I stumbled upon the Vapor Canister. It was pretty old so I just replaced it and the bucking/surging went away. I'm still having some idleing problems which appears to be a completely different problem.

Steve

Just found the problem with the idle on my 88 duke; the two sections of the throttle body were separated by about .010" or more. I’ve read before that this can cause problems with the idle and I previously checked the torque of the two Torx bolts that hold the sections together and the two bolts that hold the throttle body to the manifold. All were tight but the two sections were still loose. The only indication of this was a brown stain at the seam of the two sections.

The leakage was caused by shrinkage of the gasket between the two parts. The shrinkage could not be compensated for by tightening the Torx screws because thread lock was used during assembly. Over the years the thread lock hardened to a cement like substance above the threaded hole so the bolts could not be forced in any further. The only bolts holding the sections somewhat tight were the ones attaching the assembly to the manifold. Those alone were not enough to prevent leakage at the seams.

The problem was very apparent once the Throttle body was removed from the manifold. The top was so loose that it rattled. I had to soak the bolts in solvent for a few hours and the work on them with a small wire brush to get threads clean. I didn’t use thread lock during reassembly but plan to go back and re-torque the bolts in a month or two and will put some on then.

Also put in a “throttle body tune-up kit” while I had the part off. The kit is similar to the old carb kits, lots of gaskets you don’t need and some you do need aren’t in the kit. In particular you will need the plenum gasket that goes between the air filter housing and the throttle body and the o-rings that go on the fuel supply and return lines. Maybe some kits come with those parts but the Niehoff (Borg Warner) one I got did not.

The difference in the idle is amazing! It’s near perfect now when before it hunted, was very unstable and had what sounded like an occasional ignition miss. I think this problem is very common in the throttle body engines and is often mis-diagnosed.

To those who disconnected the EGR hose, I too previously noticed a slight vacuum on the EGR port during idle which was strange cause the port is above the throttle plate. We have emissions tests here so simply disconnecting and plugging the hose was not an option. Now that the two sections are tight, there is no vacuum at the port during idle. Disconnecting the EGR may be masking the real problem.

quote Originally posted by spark1: To those who disconnected the EGR hose, I too previously noticed a slight vacuum on the EGR port during idle which was strange cause the port is above the throttle plate. We have emissions tests here so simply disconnecting and plugging the hose was not an option. Now that the two sections are tight, there is no vacuum at the port during idle. Disconnecting the EGR may be masking the real problem.

Interesting. There should be no EGR at idle. Mine would idle just fine most times, then an intermittant stumble. Just off idle was a big stumble too. One thing for sure, the Duke doesn't really like EGR when incorrectly metered. I've had other engines that performance would degrade a little from a bad EGR system, but these Dukes will really run like crap.

I'm going to tear it apart when I get some free time and see what I can find. I do know that it idles and runs perfectly with the EGR bypassed. I couldn't be more pleased short of a Northstar conversion.

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Competition Yellow 84 2.5 Bone stock right down to electrical gremlins

[This message has been edited by Joe 1320 (edited 02-20-2006).]

quote Originally posted by Dodgerunner: By the way what aldl interface/software are you using. Just would like to know in case I get a L4 some day.

The cable I have been selling in the mall section and winALDL will support 84-86 2.5 Fieros as well as all V-6 Fieros. The 87-88 2.5 uses a different baud rate which requires a different cable. When I was trying to log my 88 2.5 I was unable to locate any software that would support the ECM so I finnaly gave up. There was someone here who had made some headway in logging the 87-88 2.5 ecm, but I don't know if they ever finished it.