Still working some small bugs out of this car. Considering it didn't run and was rotting at the PO's shop I think she has come a long way. This is probably not a big deal but it kind of annoys me. 88 Iron Duke auto. When stopped and in gear/drive my idle speed is right on 500 RPM. Seems low to to me. It is a nice smooth solid idle butjust low. I can hardly tell the motor is running. Every other FIero I have owned had/has a Duke in it. And every one idled at 800-1000 RPM in gear at a stop. Is there any way to bump it up some?

This little car went from this





To this.





Thanks folks.

Curly

Well, someone could have changed the idle, but I doubt it. Is the plug still in the idle stop screw? Try this first.... spray some TBI cleaner in the TBI, cleaning all the ports. Then run some seafoam down the throttle opening with it running. You may just have some carbon buildup. I had this issue with my '88 and this fixed it. Now.... later, when I had a low idle and cleaning the TBI didn't work, the injector was going south and a replacement brought the idle back up.

quote Originally posted by jaskispyder: Well, someone could have changed the idle, but I doubt it. Is the plug still in the idle stop screw? Try this first.... spray some TBI cleaner in the TBI, cleaning all the ports. Then run some seafoam down the throttle opening with it running. You may just have some carbon buildup. I had this issue with my '88 and this fixed it. Now.... later, when I had a low idle and cleaning the TBI didn't work, the injector was going south and a replacement brought the idle back up.

Good point I have not gone thorugh the throttle body yet. I did replace the injector though in an unrelated incident. The IAC is new too. That port looked clean when I replaced that. Also yes the idle stop has been compromised.

quote Originally posted by Curlrup: Good point I have not gone thorugh the throttle body yet. I did replace the injector though in an unrelated incident. The IAC is new too. That port looked clean when I replaced that. Also yes the idle stop has been compromised.

In that case, pull out the factory service manual and reset the idle. There is specific instructions on how to do this. Do you have the manual?

The throttle stop adjustment screw can't make the engine idle to slow.

1 - Could the tach be off?

2 - Does the engine idle faster cold and slower warm? If so that shows the ECM has some control over the IAC.

3 - Do you get a low idle speed error when the engine is idling too slow? You should. If you don't then the ECM is thinking the engine is idling the correct speed. Why? Is the ICM sending extra pulses to the ECM? Is the ECM picking up spark plug pulses on the low voltage side? That could be caused by close running spark plug wires to low voltage ICM wires. It could also be caused by a bad coil pack, high resistance in the secondary wires or bad spark plugs.

..In my Fiero wet dream fantasy I have your problem,,if the car idles at 500 rpm in neutral & you have a new IAC !! & the engine basicly runs good ??
check timing ,first paint timing mark on pulley with white paint ,,use a paper match stick or use something you can make small mark precisely along the timing slot,,.if the mark on the pointer plate is not clear mark it
you can run a nail or sharp screw point to make it more visible,or paint
install clip at console alcl as per instruction in manual to set timing
if timing is spot on advance 2 o,have timing set to advance side
you want the mark to align perfect dead center,the mark dances around but you guesstimate..
retarded timing will cause the engine to run at lower speed
low idle is ECM ,,or non emc related
sometimes with age the EMC gets slow in conjuction with the 02 sensor,not a serious problem
I see you on the forum ,so im sure you have gap spark plugs at .060
1000rpm is much to high .

quote Originally posted by uhlanstan: ..In my Fiero wet dream fantasy I have your problem,,if the car idles at 500 rpm in neutral & you have a new IAC !! & the engine basicly runs good ?? check timing ,first paint timing mark on pulley with white paint ,,use a paper match stick or use something you can make small mark precisely along the timing slot,,.if the mark on the pointer plate is not clear mark it you can run a nail or sharp screw point to make it more visible,or paint install clip at console alcl as per instruction in manual to set timing if timing is spot on advance 2 o,have timing set to advance side you want the mark to align perfect dead center,the mark dances around but you guesstimate.. retarded timing will cause the engine to run at lower speed low idle is ECM ,,or non emc related sometimes with age the EMC gets slow in conjuction with the 02 sensor,not a serious problem I see you on the forum ,so im sure you have gap spark plugs at .060 1000rpm is much to high .

88 coupe has the timing controlled by computer.

forgot Later dukes have balancer dampner
make sure this has not shifted..place a paint mark down the length so you can see if it separates this is a problem with many cars
eyeball it make sure it is tight & not separated
yup,forgot about the coil packs on 87/88 & i use to have one

[This message has been edited by uhlanstan (edited 01-20-2012).]

quote Originally posted by jaskispyder: 88 coupe has the timing controlled by computer.

He is correct - are you getting a check engine code telling you something is wrong. If the PCM can not adjust the idle rpm actual to close to what is commanded by the PCM, it should set a code.

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87 Formula Clone, 3800SC, 3.4 Pulley, 4T65E-HD, HP Tuners, AEM Wideband, 12.98 at 103.4 1/4 mile, Regal GS Gauge Cluster, S-10 Brake Booster Upgrade.

Are you sure the tach is accurate? I'd suggest getting a second tool to measure before you start "making adjustments" and spending money trying to diagnose an imaginary problem.

quote Originally posted by phonedawgz: The throttle stop adjustment screw can't make the engine idle to slow. 1 - Could the tach be off? 2 - Does the engine idle faster cold and slower warm? If so that shows the ECM has some control over the IAC. 3 - Do you get a low idle speed error when the engine is idling too slow? You should. If you don't then the ECM is thinking the engine is idling the correct speed. Why? Is the ICM sending extra pulses to the ECM? Is the ECM picking up spark plug pulses on the low voltage side? That could be caused by close running spark plug wires to low voltage ICM wires. It could also be caused by a bad coil pack, high resistance in the secondary wires or bad spark plugs.

Yep higher rpms at initial start up. The tachometer seems to be on the money. It has new plugs and wires. It is possible I have them routed around the ICM lines. I will check. I also have some spare coils I could try too. No codes are being thrown at all it is running as happy as can be. Runs really good. Thanks for the input. Also I do have the manual so I will do an idle rest too.

[This message has been edited by Curlrup (edited 01-22-2012).]

quote Originally posted by Curlrup: Yep higher rpms at initial start up. The tachometer seems to be on the money. It has new plugs and wires. It is possible I have them routed around the ICM lines. I will check. I also have some spare coils I could try too. No codes are being thrown at all it is running as happy as can be. Runs really good. Thanks for the input. Also I do have the manual so I will do an idle rest too.

How are you verifying engine speed? My timing light has a tach function in it, or I suppose you could use an ALDL cable. If neither of those works, you can use a "regular" aftermarket four cylinder tach with a DIS engine.

quote Originally posted by KurtAKX: How are you verifying engine speed? My timing light has a tach function in it, or I suppose you could use an ALDL cable. If neither of those works, you can use a "regular" aftermarket four cylinder tach with a DIS engine.

You are right I do not know for sure. I'm comparing where that needle is under load and driving conditions compared to where it is on my other 88 Duke with an auto. The exact same set up. However yeah you never really know until you check it with something else. My other 88 duke could be off too. I'll figure something out.

..The leading cause of low idle are the IAC & large air leak
a small leak causes high idle ,but if the brake booster filter is disconected this will cause a large leak.
the IAC is a controlled leak
if you have advance auto parts IAC,many of these have not acted correctly,bwm,brw brand or something like that,they have had low idle & early failure.
next is retarded timing
I would not supect the coil pack if the car runs good at acceleration & speed,,90% of time a bad
coil first shows up under acceleration or at speed.or hard to start..
the 88 duke will run on one coil pack(2cyl),just hard to start
if you can not locate problem??
...the IAC can be ajusted to raise idle speed, just a 1/4 turn,if it is IAC you would let in more air...
before you mess with IAC make sure entrance area of TBI is clean, no carbon coke deposits
you have owned other dukes but they idle to high..I am not sure you have a problem,,as long as the car does not stall frequently.
..If you replace a part later on & the car speeds up at idle, you reajust IAC

[This message has been edited by uhlanstan (edited 01-21-2012).]

Went to the orge site & also check the RPM your engine should idle at
you can go to the orge site & read how to set Idle it is a pain in the sphincter
the idle for your car is 550 to 650, I feel your tach is fairly accurate just from your post
I would love to have your problem..

jumper ADLC terminal A & B
turn key on with engine off,wait 45 seconds
this will close IAC pintle
unplug IAC while key is still on
turn key OFF,remove ALDL jumper
start engine,set idle stop screw
shut engine off ,plug IAC back in.

,,I do not think there is any thing wrong with your Idle ,,
I think there is some small problem & when it is repaired your idle will jump 50 rpm ,
,if your idle is close to 550 rpm ,if it is above 500 you are fine..

[This message has been edited by uhlanstan (edited 01-22-2012).]