Smoke test done with a bicycle pump (and smoke, of course) connected to brake booster line: no vacuum leak located. Screw under throttle body was tightened to the maximum, it doesn't seem to affect anything if I loosen it...

Wow, this I didn't know. That's exactly what happens, when I try to start the car too often, it "buzzes" if I leave the key ON afterwards. I'm definitely going to have to search...

Done! Cleaned the IAC with brake cleaner, then sprayed WD-40 inside (and opened/closed a few times afterwards). No change whatsoever.

The adjusting screw under the TB was tightened all the way. I loosened it half turn (while the car was running). That screw doesn't seem to affect anything...

This is interesting. I don't think I've got any electrical issue (I hope not!), both fans work correctly... But I couldn't find any good combination with the TB screws. I'm going to search for TB adjustment.

Do you guys think all this could be part of the tuning with the rotary shop I was planning to get?

 

did you reset that screw you were messing with to adjust the idle? It should just touch the lever and an additional 1/4 clockwise turn. After that check your tps to make sure it's correct.

 

Yes. If you've ruled out other possible culprits, it's probably the PFC. IMO, the PFC does not idle well and you need a good tuner to set the idle map correctly

 

Aint no shame in escalating after all that effort. Might learn even more with their help.

 

This morning I did exactly what you said. No change whatsoever. Had to tighten the screw I was messing with so I can leave the gas pedal alone. Bouncing idle is still there.

I already contacted them to ask, but I feel like the problem could be more than just the PFC map...

Yes that is true. But I wouldn't be as proud!


This morning, I ran out of ideas. I lazily tried to spray brake cleaner around to check for vacuum leaks.

It seems like there is a little something around the LIM gasket area (worst area ever, of course).

I've got a spare (used) LIM gasket. I think there are 2 models for these gaskets, mine are triple metal sheets (both of them).

For sure it is not right, but could it be the only reason to my bouncing idle?

 

With that much brake fluid sprayed it's possible it's seeping through the gasket or it could be the injector seal. I prefer using starting fluid instead of brake cleaner for that test, it evaporates faster and you can near immediately hear a change when it gets sucked in.

Also, some times brand new engines will idle weird until they are broken in more.

I can't remember, is the engine ported or not?

Dale

 

just read through this whole thing, that is a lot to go through.

you need to re-adjust your throttle body to factory specifications and then adjust the air bleed screw behind the throttle body at the bottom. it will take some trial and error to get the engine to idle without turning the throttle stop screw but that is the way to do it. essentially you should be able to get the engine to idle warm without the isc then introduce the isc to handle varying loads. I have my half bridge turned out 2 turns and that seems to work fairly well, yours will probably require less.

intake tract leaks will cause a higher then normal idle and possible hunt but the engine should stay running. your engine is not getting enough air and probably has a high isc duty %.

 

Are you saying that it is normal that brake cleaner goes through the gasket? I just spent 5 hours to change that gasket with another used one that I had: SAME exact issue. I cleaned it before installing it. I managed to get the engine to die (and it idles at 1,600 RPM) by spraying a lot of brake cleaner! Bad day at the office. Should I buy a new gasket and redo the job once again?

Engine is street ported yes.

Here is a picture of the freshly removed LIM gasket. By looking at it, it seems to be leaking right where I sprayed brake cleaner.




This morning, I adjusted the TB:

1. Screw in FRONT of the TB: when it touches the lever, 1/4 turn more.
2. Screw UNDER the TB: all the way in, minus 1/2 turn.
3. TPS directly: adjusted to be within specs.

Didn't change anything. Couldn't leave the gas pedal. I had to tighten the screw in FRONT to get an idle.

Thanks for your help. But I'm not sure what do to next.

Can I repeat that the bouncing idle only happens when car is warm?

 

leave the throttle stops at the proper adjustment and move the idle air screw out more. it will take a few iterations of starting and dying to get it right. but you should be able to open that to the point where the car will idle without propping the throttle open with the stop screw. mine is at 2.5 turns now to get my isc duty down under 40% on my half bridge port. my old pfc idled the car as well with the right timing. try opening to 1 turn and see what happens. timing will also help idle the car but you need to get it running on its own without touching the throttle stop. if you don't already have one a datalogit is going to be a big help in getting that ecu dialed in.

 

You don't have to turn the screw in front to get idle. That's the wrong screw. Turn the screw under the tb to get a higher idle

 

The metal LIM to block gaskets are typically useable many times. The ridges in the metal compress to have it seal. Also want to be certain that both gasket surfaces are totally flat, that there isn't a little lump of RTV, some remains of an old paper gasket, etc. there.

It can also I think be installed backwards and will have problems if so, but I think it's pretty obvious if it's backwards.

A heavy dose of brake cleaner could work down through the gasket. It's kind of like how penetrating oil can soak into the threads of a rusty bolt. That's why I prefer using starting fluid, it evaporates much faster and is more of a gas, the vacuum sucks that gas in and you notice the change in idle.

The fact that you can at points get the idle normal is ruling out a vacuum leak. If you had a LIM gasket leak it would never idle low since it would be sucking in air to raise the idle.

I think you may need to re-visit the throttle body setup as stated. Also worth checking all the switch inputs on the PowerFC - brake switch, clutch switch, neutral switch, electrical load, etc. I know on a stock ECU if you have a bad clutch switch you can have a bouncy idle, I can't remember if a PFC will do that. In the sensor check screen that's super easy to test.

Dale

 

I cannot adjust the screw under the TB. Engine cannot idle no matter how I tighten or loosen it. When it's already started, I can feel the idle raising (a little bit) when I loosen it. My only option is to use the screw in front of the TB.

I don't have a Datalogit.

Threw under TB isn't enough to get the engine idling.

To be honest I cannot really get the idle normal. When I manage to get the idle low (when car is cold), it doesn't feel like it's running alright.

My car is a JDM. I don't think there is a clutch switch on JDM cars (I have always been able to start the car without touching the clutch pedal).

I tried to play around with electrical stuff with that bouncing idle, without success.

I sprayed starting fluid around the LIM to engine gasket, and idle drops. Same exact place than before. Are you sure it can be installed backward? I quickly cleaned the LIM before installing the (2nd) gasket back. I'm pretty sure there's a vacuum leak there, but I don't know how to fix it. I mean, yes I used 2 used gaskets, but the fact that they both leak at the exact same place doesn't sound right to me.

 

Also, this is a totally different subject. While I'm spending time on my bouncing idle issue, I would like to fix that 2nd problem too. I even thought about starting a new thread for it.

My CPU #2 (F100) is bad (see very first post in this thread for classic symptoms).

A local guy told me I could simply buy a '96+ CPU #2. "It's a direct fit and basically never fails." I searched for his idea but I didn't find anything about it. What would you do?

1. Buy a new CPU #2 (VERY expensive).
2. Buy a used CPU #2 (it seems lots of people are selling failed CPU #2s).
3. Buy a '96+ CPU #2 (I like the idea).

What do you think?

 

#2 Buy an used one.
if you are sure about the 96+ will work , why not just get the 96+ CPU.
We have some good sellers here that will give your money back if the cpu doesnt work.

 

That's probably gonna be #2, because I am not sure the (updated?) '96+ CPU #2 will work as a direct fit.

 

I *think* the JDM cars didn't have 1 of the 2 clutch switches. There is one that prevents you from starting the car without the clutch pedal being down and another that simply reports to the ECU and the cruise control if you have the clutch down. You should have the second switch.

On the PFC sensor check screen you can see CLT, that should light up on and off when you push the clutch pedal down. If not the spring could be bad, you can easily fix it with a spring from a clicky ball point pen believe it or not. There's some threads on that out there.

As far as the idle air adjust screw under the TB opening, that sets the amount of air the ISC gets. If the ISC is not working (not plugged in, bad wiring) that screw will do nothing.

I'm not sure about the probable vacuum leak. Could it be air getting sucked in around where the primary or secondary injectors meet the lower intake manifold?

Dale

 

I will confirm that there is only 1 clutch switch in jdm cars and +1 on the ball point pen spring. I did it and it works well. I thought that screw was independent of the ISC and the ISC get air from another port. otherwise how do folks eliminate the ISC? if that is the case it would make sense why adjusting the screw would not have an effect.

 

People who get rid of the ISC basically set a hard throttle stop to crack the throttle open to set an idle. You don't have any idle compensation for load at that point. IMHO removing the ISC is just silly - it's not in the way, it weighs nothing, and it does its job well.

The idle air adjustment screw does adjust the air, I'm not certain if there's some air that gets to the ISC with it screwed all the way in, I've never had to dig that deep into the system.

There's a port at the entrance of the throttle body on the "floor" of the bottom inlet to the bottom throttle plate, that's where the ISC pulls air from. Typically on a running car with the TB elbow off you can put your thumb over that hole and the call will stall out.

Dale

 

good to know. I knew about the port for the air bleed screw but I never really inspected where it went. I guess i just assumed it was a separate air circuit from the isc. fwiw I kept my isc as i saw no reason to do away with it and plenty of reason to keep it. so it sounds like the OP has a problem with the isc motor and or circuitry that is preventing it from controlling idle. either way setting the throttle stop is really not the right way to do it as the pfc has idle control strategies that will not activate unless it sees a 0% tps reading.

 

I don't believe in the clutch switch idea. I pressed the clutch a few times to see if there was any difference in the idle, and no change whatsoever.

Vacuum leak in the LIM to block area is a sure thing. It could come from the secondary injectors to LIM seals (even if I already changed them before my first rebuild - brand new), they don't seem to be in the greatest condition.

I'm confident there's a vacuum leak. My problem fits exactly with the classic LIM to block gasket leaks: high idle and bouncing idle.

Today I removed the LIM once more.

Block side is nice and flat. Gasket doesn't seem too bad in my opinion. LIM surface is definitely worn. The worst spot is right where I was spraying brake cleaner (I've got lucky to spray it right there to be honest).

I'd say there are moderate scratches. My nail cannot catch in them. What do you think? Can I send my LIM to a machine shop?

 

LIMs should be a dime a dozen. Not sure in Canada though

A paper gasket may block those tiny scratches. A metal one may not conform enough. For peace of mind, i'd machine it if you can't find a replacement

 

That's why I was thinking too! paper gasket could probably be fine (but I will never do that in this area).

I quickly looked and yes, used JDM LIMs are fairly cheap.

But a resurfacing would be much better.

I just want to make sure that it will not disturb fitment somewhere else... piping before intake tube is all custom (FMIC) (and I'm not really worried about that part)..

 

How does the engine side of that gasket look?

Those scratches shouldn't be enough to be a vacuum leak. At least how it looks in the picture.

Did you figure out if the intake manifold gasket could be installed backwards? Again I don't think you did, I'm just curious .

If you are concerned with that surface you could either machine it or just do a skim coat of RTV to fill in the gaps.

Dale

 

Gasket looks OK, both sides. I think it would be overkill to change it. Very reusable.

I looked the surface with a straight edge today. I cannot see daylight through it. I will wait before sending it to a machine shop. To check for vacuum leaks, I will not reinstall the turbo (only the oil lines going to it). I renewed RTV from LIM block-off plates, carefully cleaned everything.

Lower intake manifold gasket cannot really be installed backwards.

Today I ordered 2 secondary injectors insulations. But I still feel my old ones are reusable.

I removed both injector diffusors, changed their o-rings with Atkins' o-rings.

I'm pretty sure that the insulators weren't installed properly. I had to stretch them quite a bit to get them just like on the picture, but then they definitely don't fit. Something isn't right and I don't get what it is. It's either I stretch the o-rings over the fuel rail (like on the pictures), but then I can't get them to fit in the holes, OR I install them directly in the holes (top of the diffusers, don't need to stretch them), but then they don't fit the fuel rail.

 

The injectors should fit squarely in the hole with the insulators (injector grommets). If they’re bulging out like that, that will cause a HUGE vacuum leak and cause the car to run like doo doo butt. Make sure your air bleed sockets (brown things) are all the way down in the injector holes. They DO have an orientation that they’re supposed to be installed so they have a notch on them and a little white paint dot IIRC. The grommets have a mark I think too. You can probably stretch them lightly onto the rail and then lube them up with some petroleum jelly. Then with a bit of firm pressure and wiggling, they should fit squarely into the holes with no bulging. Don’t use the bolts to “press” the rail down. Seat the fuel rails by hand and then install the bolts to secure them.

Matt