Archived eratic idle?

[PCoady]

This morning I started my truck up and went and drove my wife to work and when I got home and was letting egt's cool down I noticed my tach jumping up and down about 800-900rpms only when in park or neutral when in gear it idles fine when you first start it it jumps rpm's even worse, checked the codes and it only threw 1693 the truck has full power when driving any idea's?

I really hope this isn't an injection pump because just had new put in 8000 miles ago and also have a pusher pump so I don't know whats going on here.

 

[JLandry]

Is the engine rpm actually increasing and decreasing... or is it just the tach needle indicating erratically?



Just a stab in the dark...



How about the crank angle sensor? Has it ever been replaced?



Good luck,



John L.

 

[PCoady]

the rpms jump and decrease when idling truck still performs good with no flat spots and I just changed the fuel filter and still no improvement

 

[PCoady]

I'm wondering if maybe one of my injectors are acting up and cloging up some while at idle since it stops once its in gear or with a load on it

 

[mfburns]

If it clogs at idle why would it clear in gear or under load?? If it cleared why would it clog again under idle? Just my thoughts on your last comment.

 

[JLandry]

I'm wondering if maybe one of my injectors are acting up and cloging up some while at idle since it stops once its in gear or with a load on it

Do you have a code scanner that can display ECM information real-time (like the ScanGauge)? If so, you may want to examine what the APPS (Accelerator Pedal Position Sensor)... a. k. a. TPS (Throttle Position Sensor)... output is when this problem is occuring.



A defective APPS could conceavably cause the symptoms you've been experiencing. The code scanner might show if the TPS output is jumping around. But... the APPS also has an internal electronic idle validation switch which tells the ECM the engine is at idle no matter what the TPS output is. If the idle validation switch goes bad, I'm not sure that would necessarily show up on the TPS output. You might just want to consider replacing the APPS outright to see if the problem is eliminated. There are a couple of threads running here on the TDR discussing inexpensive APPS replacement options:



Anatomy of the APPS



Anatomy of the APPS - The Sequel



If replacing the APPS doesn't work, I think I'd start by replacing additional sensors one at a time and it really couldn't hurt anything to have the originals as spares if it turns out they aren't the problem.



Start with the IAT (Intake Air Temp) sensor, then try the MAP (Manifold Air Pressure) sensor, then the Crank Angle Sensor (the hardest to reach).



Good luck,



John L.

 

[PCoady]

today the truck finally threw a code but it threw the 0234 overboost code? would this in any way be a guide to maybe a sensor is going bad? or is dirty and needs cleaning because once the truck has a load on it it have full power and don't idle rough while in gear. It also doesn't idle rough when its started up and its a liilte cold it won't idle rough until the engine temp gets to about 140*

 

[JLandry]

today the truck finally threw a code but it threw the 0234 overboost code? would this in any way be a guide to maybe a sensor is going bad? or is dirty and needs cleaning because once the truck has a load on it it have full power and don't idle rough while in gear. It also doesn't idle rough when its started up and its a liilte cold it won't idle rough until the engine temp gets to about 140*

Well I suppose that code could relate to your problem. According to the Dodge powertrain diagnostic manual...



P-0234 TURBO BOOST LIMIT EXCEEDED

When Monitored: Ignition on.



Set Condition: Engine Speed >2200 RPM, No intake air pressure sensor out of range DTC’s present.​

POSSIBLE CAUSES

WASTEGATE MECHANICAL FAILURE

WASTEGATE STUCK​

Maybe you should check the turbo wastegate to see if it's stuck (search the TDR forum for discussions on how to check).

 

[PCoady]

Just replaced that camshaft position sensor and the map sensor and I still have the rough idle, I am completly lost it still has no codes and doesn't hurt the performance of the truck just the rough idle I need to get it fixed I'm going on a 1600 mile trip in july and don't trust the truck to make it! HELP!!!!!

 

[JLandry]

Just replaced that camshaft position sensor and the map sensor and I still have the rough idle, I am completly lost it still has no codes and doesn't hurt the performance of the truck just the rough idle I need to get it fixed I'm going on a 1600 mile trip in july and don't trust the truck to make it! HELP!!!!!

What about the APPS and Intake Air Temp sensors... have you replaced those as suggested earlier?



John L.

 

[PCoady]

I replaced the air intake sensor but not the APPS yet I'm going to test it first by checking the voltage of the #23 pin on C-1 pcm and then check the white tag on the APPS to make sure they match first

 

[JLandry]

I replaced the air intake sensor but not the APPS yet I'm going to test it first by checking the voltage of the #23 pin on C-1 pcm and then check the white tag on the APPS to make sure they match first

So you've done the following already... right?

• Replaced IAT sensor
  
• Replaced MAP sensor
  
• Replaced Crank Angle Position sensor
  

Since you got that P0234 DTC, have you verified the turbo wastegate valve is opening and closing normally?



Regards,



John L.

 

[PCoady]

Yep. I had the code cleared and it never came back up so I haven't checked it out yet I've been driving it a week now since it first started acting up but I dont trust it to go far and I've took it to a diesel shop nearby twice and they had no idea what was wrong with it either since it won't throw any codes too give us a clue. I'm not a big mechanic but would the wastegate really just hurt the idle but not have any effect on wide open throttle because that s what has me confused is the fact it idles rough but has no surgeing or missing or reduced performance under full load

 

[JLandry]

... but would the wastegate really just hurt the idle but not have any effect on wide open throttle because that s what has me confused is the fact it idles rough but has no surgeing or missing or reduced performance under full load

I'm not sure if the boost DTC is directly related to the erratic idle or not, but the fact that you even got the code is highly suspicious. I could imagine a situation where if the wastegate were sticking partially in the open or closed position it could affected the idle.



How's your fuel pressure? Does it change durring the erratic idle?



You could try turning off or removing your programmer and see if that helps.



Could be a bad injector(s). Read this thread:



rough idle/miss - TDR Roundtable



John L.

 

[PCoady]

I think the reason my overboost code threw was because I used to have a powerpuck on the truck and for some reason everytime I unhooked the powerpuck that code would be thrown and I would take it and get it cleared and it would do the same thing everytime i would install it and take it out. But it could be the injectors because I bought some about 2 months ago from pensacola diesel in florida maybe thats why they were so cheap, thank god I kept my old stock set. I'll check the wastegate still but I think I might swap out injectors and see what happens

 

[rkressg]

This might be a dumb thing to say, but maybe valve lash??? The last time I set my lash, it was out far enough that it did make a difference in the overall running performance, and it did seem smoother.

My truck idles like it has a cam, but I think it a combination of a Hot Rod VP44, Bully Dog EDM 4s, Smarty on 9, and a TST PM3 on 9. It has always been like that, but it has never broken down.

 

[PCoady]

I still haven't got it figured out but it still runs fine so I guess I'll just drive it until it starts acting up worse or it will throw a code so I can get an idea of what it is causing this. I took it in to a couple of shops and they scaned it and there was nothing and they had no idea what was wrong with it they suggested it may be bad fuel but I filled it up just recently and still idles rough. I want to get it fixed before July though because I go on leave for 30 days and I'm driving home to Michigan from Montana and don't want a problem long the way.

 

[Missouri Mule]

In my 96 service manual (for 12 valves) it states a defective or misadjusted pump timing could cause engine surge at idle, rough idle (warm engine)... .



I will try and research in gassers service manuals I know I have read/heard of this before (maybe experienced it).



I found this in an old basic repair manual, enigine surges or runs uneven; fuel restriction, dirt or water in fuel.

My other books contained info on surging at high speed.



When is the last time you adjusted valves?

 

[PCoady]

I haven't adjusted them since I bought the truck I've only put 10,000 miles on since I bought it and don't know If they were adjusted before the truck has 97,000 miles on it

 

[MHammond]

Try adjusting valves, made a big difference in idle on my previous 98. 5 CTD