Engine/Transmission (1998.5 - 2002) Throttle issue - Idle to 2000+RPM...HELP

[prob]

Brand new to these forums ... great resource!Thx in advance for any help.
Situation: 1999 2500 SLT, stock 5.9 w/ 245K miles. Recently started doing this - starts normally, then barely touch throttle and RPMs go from idle right to 2000 plus. Fuel filter is very recent; no codes; have disconnected batteries to reboot ECU; started thinking TPS so I replaced that - no joy. Any ideas?

 

[PC12Driver]

After it runs up to 2,000+ rpm, does it return to idle with your foot off the pedal? Is the idle steady? When it runs up is it running smoothly (not missing)?

I would have went for the APPS (TPS) as well. An easy check would be the ground straps between the engine and battery, and the body, frame, and battery. The APPS is based on voltage, and a bad ground could mess with that. Although I'd also expect bad sensor voltage codes with a bad ground, but can't say for sure. It probably wouldn't hurt to find all the straps and pull them apart and clean them.

Maybe pull the vacuum line going to the cruise servo to eliminate a problem there. I can't see there being a problem with that, but at least it would be eliminated.

After that I think it gets expensive. The only things that control engine speed are the APPS, ECM, and VP44.

 

[prob]

Thanks PC12!
Yes, it returns to idle w/ foot off, the idle is steady, and seems to run smooth at higher (I don't keep it there). I'll check the grounding, and I may try a different code reader in case mine's ineffective.

 

[prob]

Not knowing anything about a VP44, it seems to me that it would have an internal 'governor' or some sort of regulator to control the fuel flow to the injectors. (Am I even on track?) If so, could that be at fault? As stated before, engine idles smoothly, but I can put just a little pressure on the throttle linkage and it goes 'wide open'. Based on what I've read, I would think that an injector pump going bad would feed fuel erratically. (Again, I'm a newbie here.)

 

[PC12Driver]

There's no mechanical governor in the VP44 - that's all handled electronically.
Since it returns to idle I don't think its pulling oil or fuel vapors from anywhere to supplement the fuel it's supposed to have. How about when it runs up, does it stop when it hits redline (about 3,400 rpm no-load)? You should be able to hold your foot to the floor and it will not exceed this rpm.

 

[SnoKing]

I would disconnect to batteries. Remove the ECM connectors spray with contact cleaner. Coat with dielectric grease and reconnect. Hook the batteries back up. Turn the key on and slow press the throttle to floor and back up three times to calibrate the APPS. Turn the key off then start and test.

Did you calibrate the new APPS when you installed it, include setting the idle voltage? Did you use OEM or Timbo's APPS?

Chris

 

[prob]

Thx again PC12,
Since trouble started, I haven't red-lined the tach, haven't had it above about 2800.

Snoking,
I'll try the ECM connectors next. I did calibrate the "BRD" brand APPS/TPS when I put it on, but only ran the pedal cycle once. Checked the idle voltage - .6V as it should be.

I'm working slowly on ground contact cleaning, and general moving in and around - lower back surgery 4 months ago!

 

[prob]

After going through connections, etc., I replaced the fuel system relay with a known good one, and so far so good! Too easy! I just hope it's as simple as that!
Thx to you guys for helping a forum newbie!

 

[PC12Driver]

Outstanding! I wouldn't have even guessed that one. Nice and easy on the back, too.

 

[prob]

Thx again, PC12!