I'm having some weird issues with my TPS and fuel delivery during decel.

When i pulled into work today, my rpms jumped to 2,000 during idle and just stayed there for about a minute. I pulled out my laptop and noticed the TPS was reading 18% with the throttle plate closed. Borrowed a socket wrench and adjusted the tps down to 13.3%.

Upon leaving work, when i started the car, TPS was now reading 10%. So now i'm about to go down and re-adjust it back to 13.3% again.

The 2 bolts are on there really tight so that rules out the TPS moving on its own.

I also noticed that occasionaly, my car won't decel properly while in gear and foot off the throttle. AFRs read about 12 and car feels like it has cruise control on. It decels very very slowly. TPS was reading 10% and injector pulse width was at 1.28. The injectors aren't turning off. This only happens when above 3200 RPM. As soon as the RPM come down to 3200, injectors turn off and AFRs jump to 21 and car starts to properly decel. It always happens at that exact RPM mark.

any ideas?

 

What ECU?

 

stock ecu. car was tuned a year ago and tune hasn't changed. (ecuflash)

mods:
rc 1000cc
walbro 255
cosworth m2
3" turboback

brand new oem FPR
brand new oem IACV
injectors cleaned and balanced by RC
no boost leak

 

the idle issue was resolved by replacing the TPS. It was sticking a little.

I still haven't fixed the decel issue though. I tried another ecu from an evo9 and that made no difference.

Once going into positive boost pressure, and letting off the gas above 3k rpm, the car doesn't turn off injectors. It feels like cruise control is on. If you bring the revs up past 3k without going into boost and let off the gas, it decels fine with the injectors off. All this is done while in gear.

If i use the brakes to bring the revs down, it will go turn off injectors once it crosses below the 3krpm mark. Its always happening at that mark.

summary:
- above 3k and positive boost = no fuel cut decel when lifting off until rpm drops below 3k
- above 3k and vacuum = normal operation when lifting off. injectors turn off and car decels fine.
- boost leak tested to 31psi. no leaks.

any ideas?

 

There's a long thread in the ecuflash subforum about throttle hang. It was late and I was dead tired so I didn't make it to the end. Anyway, it seems, as I recall, the problem was BOV related. I suggest you go seek out this thread

 

ya, read that thread. My BOV is fine. Holds boost till 30-31psi during boost leak test. No bucking while driving. Using slightly crushed oem BOV.

I've probably gone through every possible throttle hang, iacv and running rich thread there is..lol. People have been able to mask the decel problem by tweaking their IACV settings but thats not really a fix, just cover-up on a zit. Plus, that only gives you the feeling of decel, the car still doesn't turn injectors off.

I suspect its the MAP sensor, even though everyone says that the MAP is only used for detecting if the egr is open or not. After going into 100+ load, I think the ecu checks the map to make sure vacuum is present before shutting off injectors. I checked my MAP sensor 2 days ago and its reading 5v at 0psi which is correct but its also reading 5v at -10psi (10 psi of vacuum), which is incorrect. Its suppose to drop about 1v for ever 10psi I think. Waiting on another oem map sensor to arrive from a fellow evom member. Hopefully i'll be able to test my theory out this Saturday.

 

have you verified that the throttlei is closing fully?

be sure that the screws are tight holding the throttle blade.

i can not believe how loose 1 of the oem blade screws are, when i take throttle bodies apart for 65mm upgrades or rebuild service.

 

yes, throttle plate is on tight. Its closing completely. TPS reads 13.3% (fully closed).

I've replaced the seals with your seals which got rid of the small boost leak i had there.

 

Your summary items are normal response. I see the same thing on my Evo.

 

The car decelerated properly when i first bought the evo. While in gear, throttle plate closed and tps at 13.3% the injectors would shut off and the car would decelerate all the way from redline until about 1500rpm where the injectors would turn back on. Even after being in positive boost.

Now, the car won't shut off injectors when lifting off the throttle completely after being in positive boost and above 3k rpm. The car feels like its got cruise control on. AFR reads 12ish during this time.

This is definitely not normal operation.

 

I've got the same problem, but it doesn't happen every time. If I tap the gas it will swing back to lean and decelerate properly.

 

The fact that you can make it decel by just tapping the throttle make me think that it could be a sticking throttle cable or throttle body plate.

Have you logged TPS when your problem happens?

 

I have the same problem as hyeteck. My problem is only intermittent though.

 

ok so i replaced the map sensor.

Now i'm getting ~4v at 0psi and ~2.5v at around 12psi. Seems like he new MAP is working fine.

Unfortunately the decel problem is still there. Its a very annoying problem to have, especially on the track when you downshift and the car doesn't engine brake.

I think it might be emissions related. The ecu is trying to add some fuel to cool the cat that it thinks is still there?

Also, I noticed the EGR temps were getting lower and lower as the car warmed up. The EGR valve looks totally mechanical so I'm not sure where its getting EGR temps from.

 

Also, something that I forgot to add is that the car has cold start issues. It takes a couple tries to get it started in the mornings. The workaround is to open the throttle plate (depress the accelerator pedal) for a second and then let off and start the car, at which time it fires right up.

Both the cold start and the no fuel cut during decel issue started around the same time.