Up & down idle 88 Duke when warm

[Donster]

I sent David Brill an email earlier in the week asking what happened to The Phoenix and Purple Haze and haven't gotten a response, yet. 

Much obliged Charlie. LMK if you hear something.

BTW: Replaced MAT today, no change. :-(
Reset IAC (Used Ogre's procedure for Idle Stop.....ECM A&B shorted with ignition on, heard the IAC clicking, disconnected IAC, took jumper off A&B and turned ignition off, plugged IAC back up, disconnected and reconnected battery, drove 35 mph for 30 miles).........no change.

So now I am at a loss, might get a new EGR and take the block-off plate back out and still waiting on new spark plug cables (although there are some people here that doubt they could be the issue) :-)

Or, perhaps we can try this: Which one of you Duke Experts (Pat, Steve, Charlie?) wants to come over to Germany and help me figure this out?? LOL

Greetings from good cold ol' Germany,

\D

[Fierofool]

Or, perhaps we can try this: Which one of you Duke Experts (Pat, Steve, Charlie?) wants to come over to Germany and help me figure this out?? LOL

\D

Two things eliminate me.  Cold weather and I know very very little about the Duke.  Having made that know, I will offer this.  The high idle may be caused by a vacuum leak somewhere.  I have used a small handheld propane torch to find vacuum leaks.

The air mixer shield on the end of the torch will unscrew, leaving just the gas jet orifice on the end of the tube.  I've taken a properly sized rubber hose about a foot in length and slid it over the end, lightly turned on the valve and with the engine running, passed the end of the tube over vacuum lines and connections and around mating surfaces.  When you find the source of the leak, the engine rpm will increase.  There's no likelihood of an explosion.  The only thing that might happen is that should you get around a leaky spark plug wire, it might briefly ignite the end of the hose, but because you don't have the air mixer there, it won't stay lighted. 

Just got a text from David and he said he still has the cars and would like to find them a new home.  I asked for a series of pics and info on each and I'll put them in The Market Place for him. 

[Donster]

EGR Block-Off removed, new EGR valve arrived this morning (3 days from RockAuto in the US to Germany......not bad).
Installed it, while my hands were about to freeze off........no change, idle still hunting, but in general, the engine runs better.
Spark plug cables should arrive tomorrow morning. After they are in and it still has idle issues, I'm going to tear out all vacuum lines and replace them.

Just to recap -- 88 Duke, all original. Engine runs great, idles good when cold. As soon as it warms up, the idle starts hunting.

So here is what has been done:
All vacuum lines checked
New spark plugs
EGR valve blocked
New MAP sensor
New IAC valve
New TPS
New Throttle Body Housing gasket
New TB injector
New MAT sensor
New EGR valve

Question: Could the ignition coils also be the problem?

\D

[GTRS Fiero]

I'm doubting the ignition coils, and you replaced the intake gasket.  O2 sensor?

New IAC does not equal good IAC.

[TopNotch]

What kind of spark plugs?

[Donster]

AC DELCO R43CTS6

[Donster]

New spark plug wires installed, replaced most ground connections, still have a hunting idle.
Tomorrow I'll be at my friend's shop, will check vacuum lines AGAIN.

[Raydar]

Does your fuel regulator have an adjustment? If so, it should be on the throttle body, somewhere. I'm thinking that the pressure may be off, a bit.
Then again, if you have already replaced the entire throttle body, it should be preset.

How does the car run, out on the open road? Good acceleration with no stumbles?

[Donster]

How does the car run, out on the open road? Good acceleration with no stumbles?

Runs like a charm, even good gas mileage, no stumbles. Only thing I still need to replace is the exhaust, as it rattles when in "P" or "N".
Other than that and some electrical gremlins in the dash, it's a great little L4

\D

[Raydar]

How does the car run, out on the open road? Good acceleration with no stumbles?

Runs like a charm, even good gas mileage, no stumbles. Only thing I still need to replace is the exhaust, as it rattles when in "P" or "N".
Other than that and some electrical gremlins in the dash, it's a great little L4

\D

Okay. That would seem to eliminate a bad fuel pump or clogged filter. (Higher demand for fuel would seem to make either of those issues much more pronounced.) 
#headscratch

[Fierofool]

Just be watchful of that 4500 rpm redline.  I found it was very easy to overdo it in First and Second in my 88 Lil Duke Coupe. 

I did have a problem with high idle, and was never able to overcome it.  I don't remember, but does the 88 have an Intake Air Temperature sensor or Thermac sensor in it's intake system?  Hunting idle is usually the result of the ECM trying to correct for information sent by one of it's sensors.  An air leak will result in a lean burn.  The ECM dumps fuel and it becomes a rich burn, so it cuts back fuel.  The o/2 sensor detects a lean condition, and you get the same cycle.  All temperature sensors can be tested for accuracy, including new ones, by using a multimeter and the information in this chart:
http://www.gafiero.org/bbs/index.php?topic=641.msg4644#msg4644

[Raydar]

Just be watchful of that 4500 rpm redline.  I found it was very easy to overdo it in First and Second in my 88 Lil Duke Coupe. 

I did have a problem with high idle, and was never able to overcome it.  I don't remember, but does the 88 have an Intake Air Temperature sensor or Thermac sensor in it's intake system? 
...

It's in the intake manifold.
From Ogre's cave...
MAT sensor. 87+ 4 cylinders gain an additional sensor. The MAT (Manifold Air Temperature) sensor is located in the intake manifold to the right of the TBI unit. DO NOT over tighten the MAT sensor or you may split the intake manifold.

Ogre has probably researched the Duke as much as anybody.
http://fierocave.shorturl.com/

[Donster]

New MAT, new IAC....ordered another IAC, just to be sure, should be here by Wednesday. And of course, I made sure I didn't crack the manifold when I tightened the MAT sensor.
Like I said, will tear out ALL vacuum lines tomorrow, except for brake booster, and go from there.
The engine has really gotten better, but occasionally, the idle hunts when temp is up, which baffles me.
Still thinking about replacing coils???
Couldn't believe the improvement of radio reception, after replacing ground connections and spark plug cables. LOL!!!

\D

[Raydar]

My tired 155K Duke idles steady as a rock.
If nothing else, I'll warm it up, and start unplugging stuff, and measuring sensor resistance.
(I'm certainly not an expert on this engine. Charlie and Pat have messed with them a lot more than I have.)

Edit - I'll be really surprised if it's related to the coils. I'd be more inclined to think it's related to the DC voltage available to the ECM.
(I went back and reread the entire thread, this morning. The ECM posts were... intriguing.)

2nd edit. The "idle speed vs ECM volts can be reprogrammed", if I remember correctly. I might have to have a look.
Or it might be "injector pulse width vs volts".

[Donster]

NO vacuum leaks! Replaced the 4 (EGR, MAP, 2x fuel canister). Only one I didn't replace is the big one from the brake booster, but it checks out.
Intake manifold and TB housing are all sealed. Spent 2 hours doing nothing but hunting down possible vacuum leaks.

Question: Could it be the injector? While I'm asking, does anyone, or maybe the club, have a spare 88 L4 TB injector they could sell and ship me?
BTW: ECM has good stable power and ground.

Thanks.

\D