Speed density engine rich at idle

1az-fe Toyota Speed Density Engine
-24% STFT at idle
0% STFT after WOT snap and then back to -24%
high idle (1100 rpm, 900 when hot)

Car starts fine and road tests ok (a little sluggish on acceleration). STFT reduces to zero at various rpms during driving.

possible causes I can think of is

Faulty MAP system (reading high)
Faulty O2 system (reading high)
Fuel pressure (Too high)
Leaking/dribbling fuel injector/s
Faulty air intake/engine temp sensor
Timing???? would timing cause such drastic negative STFT?

What else could contribute to severe negative STFT on a speed density engine?

If it has an EGR valve, and it's leaking, that additional air going into the intake would increase manifold pressure and fuel.

Nissan Technician

Tutti57 wrote: If it has an EGR valve, and it's leaking, that additional air going into the intake would increase manifold pressure and fuel.

Nissan Technician

Agreed, but it will not max out fuel trim into negative?

What else could contribute to severe negative STFT on a speed density engine?

The last one I battled was a 2002 Dakota 3.9L. The EVAP vent hose was twisted and kinked.

I guess it depends on how big the leak is. Is there anything you can pinch or block off to test it?

Nissan Technician

Hello,

I think you first should stay focused on that high idle.

Maybe PCM strategy priority is to keep target rpm.

Thanks guys. I've been quite busy with this one on Iatn, there are a lot of very interesting feedback in there concerning this engine.

I'm looking now at the possibility of backlash on the camshaft based on the waveform I captured on the CAM sensor (Cylinder head over skimmed and/or stretched timing chain). I also think my timing is a bit retarded as well.

members.iatn.net/forums/search/search.as...orum2&ft=1&fv=4&qv=1

I'm going to try and post the wave forms in jpeg in this post, hope it works!

hey there, did you get it fix? quite an old post. facing same issue with one of my customer who got his car (Suzuki Cultus 1.0L) engine overall. Trims were fine before that, now its -20% at idle and gets better with high rpm and drive.