I've been having intermittent idle and acceleration problems. Sometimes the truck runs great and sometimes the idle is all over the place, the exhaust smells really rich, and acceleration is poor (accompanied by an CEL that comes on what seems like randomly). I pulled codes for KOEO and got the all clear (111) and KOER and got a 411 (cannot control RPM during low RPM test; secondary air injection). I checked the TPS voltage (replaced the TPS with a new Motorcraft unit a couple of weeks ago) and got a smooth change with throttle opening, but the throttle closed signal voltage was low (0.71 V) and the voltage in was 4.7 V.

Would low TPS voltage cause the problem resulting in the 411? Any suggestions on where to start looking for the problem?

The truck is a '92 4x4 with the 4.9L motor.

Any ideas would be great!

 

I know this thread is from 2017 but will post anyway since I have the same issue.

1992 F150 5.0. The only KOER code I have is 411. I've read up on this code description (can't control low idle) and others have suggested to look for air leaks. I can't seem to find any leaks but haven't used a smoke machine to really test things out. But this caused me to have a few questions and would love some input.

1) Should the engine idle if the ICV is disconnect ?
2) If I manually introduce an air leak will the idle run up ?

I'm more familiar with Euro car that use a MAF based air metering where an air leak will create a lean/rough low idle.

Thx, how someone can jump in.

Philo.

 

Assuming you have the MAP (not MAF) - hard for this ol' mind to keep all the years straight of when things were changed - tank and rail fuel pump combo to only a single in the tank, MAP to MAF, OBDI to OBDII, AOD to E4OD, etc. :-)

1) Idle speed should drop noticeably upon unplugging, possibly dying but definitely slower than when plugged in.
2) Yes. A small air leak may be within the control range of the IAC to offset, but a larger leak will result in higher RPMs.

Have you cleaned the innerds of the IAC? Mine would crud up and cause idle issues about every other or 3rd year, kept a can of carb cleaner at the ready, then all good again til next time.

 

Thx for the reply.., so I've replaced a bunch of stuff lately. ICV, TPS, Purge Valve, FPR, Injectors, timing gears/chain, intake plenum gasket, PCV, vacuum canister on the passenger side, lots of hoses, etc.. When I unplug the ICV there is no change in the idle rpm so I think there is a default bypass position that's keeping it running. I think I'll keep looking for vacuum leaks, I haven't check all the vacuum lines on the drivers side. There's some big lines that come off the plenum, brake booster, a roundish plastic thing with vacuum lines wrapped around it (have no idea what this is), another black coffee can canister, etc.

What if I do this, if I take the intake hoses off so I can get inside the throttle body and then block off the bypass air holes. If the engine dies I was right about a default bypass position in the case of a ICV failure, or if I unplug it. If the engine doesn't die then I have a big air leak.

Open to feedback. Thx !!

 

Updating this thread. Found the problem, the gasket for the EGR valve body slipped out when I did the injector replacement work. It was just hanging in place by one bolt. I found the issue by spraying brake cleaner on the TB and bam, the idle ran up immediately. So I looked closer and saw the hanging gasket.

so i fixed and tge idle came down to 650ish, but now theres a weird sound coming from the top of the manifold when i rev the engine. I noticed that the EGR pipe was moving around a lot. How does the pipe connectvto the intake manifold ? Should it be ridged or does it flex and move around ?

Thx..