allrotorfd

iTrader: (1)

I am having an odd issue with my FD. I've been searching the forum for a few days but I can't find anything that matched my problem.

About 2 weeks ago my car started stumbling slightly under load, accelerating from about 2000RPM-3500RPM. Then after a few days it started stumbling worse. It is much worse under heavy (WOT) load. Then shortly after that, I noticed my vacuum was lower at idle. Then the next morning when I started the car, it idled at 2000RPM until it got to operating temp (normally idles around 1300RPM when cold), then the idle started to hunt pretty bad once it was up to operating temp. Whenever I would rev it in neutral the car would rev and backfire. Vacuum very low.

Today I was checking for leaks in the rats nest and I couldn’t find anything that looked wrong. After reassembling everything, I got in the car and started looking at the PFC sensor screen. While the car was hunting at idle, I turned the A/C on and the idle instantly dropped down to 1000RPMs (which is where it normally idles). It idled perfectly and the vacuum came back up to normal. With the A/C on the APR also turned on in the PFC sensor screen. I turned the A/C off and vacuum dropped and started hunting again. So I took it out for a drive with the A/C on and it ran much better, still not perfect, but instead of stumbling there was just a slight lack of power.

Then I drove the car up to 4000RPM and let off the throttle and watched the boost gauge. I switched back and forth from having the A/C on and off, and it pulled more vacuum when the A/C was on, and would drop when I turned it off.

So the car runs much better and pulls more vacuum with the A/C on for some reason.

I have been reading the FSM and I can’t figure out exactly what having the A/C on is triggering to make the car run better.

My relative mods:
3mm Race ported engine
750cc/1300cc
PFC tuned by Jeff (Rotary Power)
No air pump
All bolt ons
Stock twins
(The car has been running perfectly for over a year with these mods and I have not changed anything)

Hopefully someone on this forum can help me out.

Thanks
Mike

Kento

I'm thinking an intake leak of some sort, possibly the LIM gasket.

yuichiror

iTrader: (1)

Wow! I have a similiar problem. When there's a "light" load on the engine, fan blower above 2, parking lights on, etc my idle hunts just a bit, maybe like up and down around 100rpms, from 800-900rpms. When I turn on the AC she's fine.
Ok, I decide to adjust my idle today, just a tad to help get rid of the bouncy idle. I ground the TEN and GND in the diag box, raise the idle by 100rpms, it smooths out a bit. So I go to blip the throttle from inside and voila! The check engine light is goin' nuts. Count the codes: 15 and 18.15 = O2 sensor, 18 = TPS-narrow range. So I think those two items are probably part of the idle issue, at least I'm sure the TPS after it's adjusted will help alot. I've been meaning to adjust the TPS for a while now, cause I was thinking that was part of the idle issue, but I've been workin' 60 hour weeks, I have a wife and four kids blah blah blah. So a funky idle was the least of my worries.

I also noticed my pressure chamber isn't being pressurized. I pull off a hose and I get NADA, no swoosh of air. At least that's not major. I did a quick check and the hoses seem to be ok, I'm thinkin' it might be the check valve.
BTW in case it makes a diff between our problems, my mods:
All bolts ons( DP, CB, IC, intake) and a mild street port.

allrotorfd

iTrader: (1)

I also just noticed, if I hold the throttle at 2000RPM in neutral with the A/C on, the injector duty cycle is about 8%. Then if I turn the A/C off, the injector duty cycle shoots up to 11% and the RPM goes up to 2600RPM.

allrotorfd

iTrader: (1)

Anyone have any idea of what could be going on?

Kento

Have you given any thought to the leaking LIM or turbo gasket suggestion? It would account for the sudden problems after a year of none, as well as the elevated rpm upon cold startup and poor vacuum, plus the hunting when warm. The ECU is programmed to raise idle with the A/C on, so that would account for some of the vacuum and idle weirdness you experience with it switched on. Just my $0.02...

yuichiror

iTrader: (1)

Have you checked for engine codes? Could lead to something. I just checked my ECU for codes and 2 came up. Both I'm sure are responsible for my issues and the last time I got a check engine light it was for something totally different.

allrotorfd

iTrader: (1)

I am going to replace the UIM and LIM gaskets this weekend, and as for the ECU codes, I am running a Power FC so I can't do that.

Thanks for the suggestions

Quickfini

iTrader: (6)

I had the exact same problem with my FD. I replaced my LIM gasket and it fixed it.

adam c

iTrader: (2)

Check your clutch switch.

allrotorfd

iTrader: (1)

I just wanted to update this thread for future reference in case anyone runs into the same problem.

It turned out to be my leading coil going bad and not sending any spark to the leading spark plugs. I ended up replacing all of the coils. The car runs perfect now.

Sgtblue

iTrader: (16)

Thanks for the update allrotor. Just curious....how did you finally narrow it down? And I'm trying to understand, but can't get how turning the AC on improved things?

allrotorfd

iTrader: (1)

Before I found the ignition problem I was thinking that it had to be some kind of vacuum leak somewhere so I took off the UIM and inspected everything and I couldn’t find anything out of place. A few people suggested the LIM gasket, but I have pulled the turbos in the past and it was not a pleasant experience, so I wanted to make sure that there was no possibility of the problem being something else before I did that.

I then started pulling the spark plugs just to make sure I was getting a spark from all of them, I didn’t expect it to have anything to do with the ignition system but I just tried it anyway, and I found I was getting spark from the trailing plugs but not the leading. I had an extra igniter so I tried swapping that first and that didn’t help, so I figured it had to be the coils.

As for the A/C making the car run better, I really have no idea what caused that. I did notice when I was monitoring the readings on the PFC, as I was switching the A/C on and off with the car idling, that the ignition seemed to be advancing whenever I turned the A/C on. Since the engine was running only off of the trailing plugs, it was having the effect of retarding the timing a lot, and maybe turning the A/C on advanced the timing a bit and helped get rid of the hunting at idle. It’s also possible that when the A/C is on, the ECU raises the idle up a bit and that was allowing more air in and leaning out the mixture.

But then again my knowledge of this stuff is pretty limited.

Thanks to everyone for your input.