Hi Guys,

Hopefully third times a charm.

My JDM FD is having some idle and fuel issues. I have ruled out the injectors after testing and recently came across a post suggesting the TPS might be the issue which has lead me down the rabbit hole but I think I am on the right track. The Boost Sensor, 02 Sensor and Spark Plugs have all been recently replaced and the engine has been fully blanked off excluding the thermowax just as an FYI. I also have a PFC.

This has finally lead me to fiddling around with the TPS and multiple screws on the throttle body. I'm hoping for some advice about the process because I cant seem to get it perfect. Below is what I have done in order.

1. I first fully closed the idle control screw located below the throttlebody because I no longer have an Idle Control Valve and as far as I am aware this screw no longer does anything after the delete?
2. I let the car get up to temperature and adjusted the throttle stop (screw 2 on most of the annotated sketches floating around). For some reason I cannot get lower than 850rpm using this method of adjustment without it running rough or hunting. This stop effects the lowest and smallest butterfly valve in the TB which i'm assuming acts as a kind of choke?. So my logic is to leave that cracked open a small amount so the engine at least gets some air and doesnt run rich. BTW its still running rich .
3. I then adjusted the throttle cable preload screw so it was just about to engage the throttle. Just to note, If I fully close the butterfly valve adjusted in step 2 I can get the idle down to around 750 but the engine becomes really rough and sometimes starts to hunt.
4. Finally I checked my TPS readings using the commander and I get VTA1:0.46v and VTA2:0.98v in the closed position which I believe falls nicely within the range specified in section F of the workshop manual. The open positions also fall within range.

To summarise with all of this tweeking I am still ending up in situations where the car runs rough or hunts in idle and also stinks of fuel. My logic says to open the "choke" valve more to prevent it running rich but if I do the idle speed obviously increases which I dont want. Since tweeking I also no longer feel the 2nd turbo kick it at around 4500-5000rpm which I cant explain. There seems to be more lower end power but nothing top end.

Any insight would be appreciated.

Thanks

 

the most important things about what you have going on.....

1. when was the power fc installed?
2. is it untuned?
3. what changed between the last time the car was running fine and now?

your main problem may be that you replaced the MAF.... if your FD has a MAF then you have some issues that no one can help you with

 

Sorry I mean the Boost Sensor. It was replaced by the previous owner but looks fairly recent given its condition.

1. When I purchased the car the only modification was a greddy intake/elbow and the typical vacuum line simplification which I double checked. The PFC has been reset on a couple of occasions and the car worked fine if I ran through the idle learn process. There were several boost leaks which I fixed around the time I started blocking things off.

2. Yes. Its running the basic PFC tune.

3. The car had a tonne of boost leaks due to brittle/broken vacuum lines as well as a cracked turbo to BOV hose so I was amazed it made any boost at all. While replacing them I took the opportunity the blank off the ACV and pretty much everything on the throttle body excluding the thermowax. I'm pretty sure my Idle Air Control valve was already faulty because I checked for continuity and was getting a 0 reading. After the fixes and deletes the car would hunt in idle when it got up to temp and judder when the throttle was closed while driving. As soon as you apply some throttle the issue goes away and the car drove fine.

When I posted the issue, I was told to have a look at my injectors as there was concerns of a leak, hence the fuel smells. I pulled them off over the weekend, cleaned and tested them. All fine. It is since I put the injectors back on and the intake manifold etc that these new issues have suddenly occurred. I've double checked all my lines and connectors, and nothing seems out of place and the boost readings look the same as usual. Not a clue why the 2nd turbo is not kicking in. I'm hoping its not kicked the bucket.

 

you have a collection of issues. an untuned power fc will do a lot of the things you are describing to include the inconsitent idle, dumping of fuel, jittering, weird on and off throttle responses.... all sorts of stuff. in addition to that, tuned or untuned the power fc will just sort of do what it wants for a while. from what ive seen, its takes a couple weeks of just driving for those things to go away on their own before everything is just consistent.

the sensor screen on the commander has quite a bit of information to help in troubleshooting. i would suggest starting with the tps. you say you calibrated it but did you use the sensor screen to do it? watching vta1 and 2 will make the calibration process remedial. no need to fuss with a multimeter.

disabling o2 sensor feedback in the settings on the commander can help with the erratic idle and other driving response issues youre having as well.

do you have a wideband installed?

do you know if you have a paper lower intake manifold gasket? take the coupler off the greddy elbow and do your best to cover the inlet fully while the car is running. the goal is to choke the motor out and get it to stall. depending on how it responds to this test will tell you how large your vacuum leak is if you have one at all at this point. seems like you had quite a few compromises in your system. its REALLY easy to miss something.

ultimately you NEED to get the pfc tuned... period. driving around on the base map is not a good idea. it will work of course but your car will not run well as you can see. you can do all this troubleshooting and fix a whole slew of issues but never reach the resolution youre looking for because of the untuned pfc.

 

Thanks for the advice Rex. I'll give disabling the 02 sensor a go in the commander and test for a vaccume leak before I dive into the other suggestions.

To answer your other questions:
Yes I used the sensor screen to adjust the TPS
I dont have a wideband installed yet.
Not sure about the gasket. I'll have an investigate tomorrow.

I was trying to hold off on on a tune because I live over 200+ miles from my nearest tuner with an FC-Datalogit. It may be worth me just purchasing one for $300 and going somewhere local. I'd probably end up spending close to $400 in fuel just making the 400 mile round trip with the current fuel prices in the UK.

Thanks again.

 

yea... if a tuner is that far from you then getting a datalogit would absolutely be worth it. get a wideband and install it. youll need to remove the downpipe to have the bung welded in the correct location. you want to be at least 18in downstream of the flange.

 

If this is a street car, put the ISC back on. If it is truly bad, find a good used one. ISC's are typically very reliable and they do a great job. You can get a solid idle with no ISC, but if you try and run air conditioning, put a load on the engine, etc. the idle will be all over the place.

You most likely have a vacuum leak between the throttle body and the engine. I have a thread talking about idle troubleshooting, find and read through that.

All the block off plates you installed have to be well installed with good gaskets and in some cases with some RTV as well. Those are typical spots for vacuum leaks. The TINIEST hole is all it takes to mess up the idle.

The primary injectors have rubber grommets around the end where it fits into the block. If they are missing, damaged, etc. you will have a vacuum leak there, that's common when messing with injectors in the car.

Before going too crazy, get a can of starting fluid, run the car at idle, and carefully and slowly spray around where you think a leak could be. When that fluid is sucked in the engine will rev up and smooth out, that will at least give you a spot to start investigating.

Dale

 

Hi Dale,

Thanks for the advice. I actually thought I had the issue figured out as the car was running fine for a while (still rich) after I went over everything. I also reinstalled the ISC as you recommended. However, the last couple of days the rough idle has returned but only after the car has been driving for a while.

At the minute I think my issue might be alternator related. I decided to add the battery voltage to my commander screen and I noticed the voltage drops to 12.4v almost instantly at a 750rpm idle and slowly starts to drop (maybe 0.1v every couple of minutes). When the idle starts to bounce the voltage drops even more. In addition when I turn on the accessories, the RPM's do not increase like intended. Obviosuly the battery is not draining otherwise I wouldnt be able to start the car after each drive which makes me think the alternator regulator is acting up and is limiting the voltage. When I apply some throttle the voltage only increases to around 13.0 - 13.2v. So my theory is, after driving a while the alternator regulator is putting out such a low voltage that when I take my foot of the accelerator the draw is so large that the PFC doesnt know how to react and eventually just stalls out or just looses power. Pretty scary when it happens while moving and you loose all power steering and breaks. Is this something you have ever encountered?

I'm tempted to put back everything I removed just to see if the issue persits. If it does than at least I know I was not to blame and it was just bad timing.

 

As alternators wear out they will put out less voltage. I think your alternator is just old and worn. You should see around 13.5v at idle when warm, you will see a bit higher voltage than that when cold, that's totally normal.

Stuff will act weird with low voltage, I wouldn't troubleshoot any further until you sort that out. Lots of stuff out there on alternator troubleshooting, the FD has a really plain standard alternator, nothing weird or fancy.

Dale

 

Hi Guys, back again with an update.

Alternator turned out to be fine. Injectors fine. No leaks on any of the vacuum lines from what I can see. Cars only boosting to 0.16 on the PFC but i'm hearing a air noise anything past 3k rpm so I may have a faulty BOV?

Anyway I came across the FSM for the throttle body on the FC's and gave it a go. When I set the primary throttle to have between a 1.1 and 1.7mm gap the car revs to 4000+. Also in that position the cam stop is nowhere near the dash pot. Should the FSM work for the FD's too or was that wishful thinking? All in all I ended up closing it back down to regain a normal idle, checked the TPS and it seemed to be running well for a minute. Anyway, I’ve noticed that the bouncing idle seems to occur when the car gets up past 80c like clockwork. If I put the AC on which turns on the fans and force the temp back down to 68c (mishimoto thermostat) the car sorts itself out. Are engine temps linked to the tune at all or is it more likely the heat is messing with something? I deleted the thermowax but kept the idle control valve. I've tried disconnecting the ICV with no change, so I don’t think thats faulty.

Mark

 

Super low boost + air noise = boost leak, hands down. You have a split coupler or a loose coupler somewhere. Fix that first.

Clean the ISC, it will get dirty over time and stick and cause the bouncing idle. Easy fix.

Dale