Idle problem

[smagnotta]

First I want to say I have no codes thrown. I replaced the AFM, engine harness, throttle body, TPS, ISC, Igniter, CPS, plugs and wires over a period of 6 months. I have the 550/Lexus mod with S-AFC Neo, ARP studs, HKS MHG.

Timing has been set correctly.

The car starts and runs fine at first but starts to stumble and miss as it approaches operating temperature. It revs fine in the higher RPM range (1,500 to 6,000) but when you decelerate and hit around 1,000 RPM it wants to stall. If you quickly accelerate and let go then it will reach around 1,000 and always stall out.

I checked the vacuum lines and found nothing loose. Vacuum is between -18 and -20 when idling.

I guess I can go around with a multimeter and check all the electronics. This car has never really idled correctly, even before all my mods 8 years ago. It always had the miss.

Update: I just used another ECU and the car seems to be a bit better - not as much stalling. However, it still has a miss at idle and fluctuates between 700 and 900 RPMs when idling.

 

[smagnotta]

Anyone have any suggestions on what to try next?

 

[tlo86]

IC pipes possibly, my car would do that when i had a tiny leak near my IC, or your IC itself might have a rupture but thats one of many possible things..

 

[the_ghost]

Anyone have any suggestions on what to try next?

We've similiar set up mine doesn't hesitate but I do the below.

Increase the idle to about 1100-1200 rpm and the safc +30% to compensate for the 550cc injectors.

Driving: Butterfly (blimp) the (gas pedal) throttle 2-3 times if the rmp drops below the setpoint after throwing it in neutral immediately after a hard acceleration. Also during a drag or roll, let the car coast in gear for a 4-5 seconds before throwing it in nuetral, if not possible, prepare to butterfly the throttle if needed.

 

[smagnotta]

The +30% S-AFC fix helped a bit but I think it's not the solution. I also replaced the EGR valve and just double-checked the ISC and it is working fine. I am at 32 PSI fuel pressure. Vacuum at idle is around 19. I set it to 10 degrees timing with diagnostic port jumped. I checked the IC pipes -- all are fine. I checked all vacuum lines and all are connected. No codes (ENG - OK).

I really thought all these new parts (which were needed by the way) would fix this problem. All 3 coil packs are brand new too. Maybe the spark plugs got fouled up with all this starting I have been doing to get the idle problem fixed.

It's really annoying that the car stalls after high RPMs, in reverse and at stop signs. I always thought it was the electronics but I replaced everything. I am really starting to think the bottom end needs rebuilt. I guess I can live with this and get the body fixed and repainted, then go from there.

Just for kicks I might check the compression across the cylinders and also check for exhaust gas in the coolant.

 

[Idealsupra]

holy crap 1st of all dont do anything 30% on the afc.... that will start messing with your timing your doing more bad then good there. not to mention to "compensate for the 550s" (WOW) you would NOT +30% you would -30%. HOWEVER you are running the lex/550 combo so they should cancel each other out being ~25% more air/fuel then stock.

it sounds to me like you have a bit of a boost leak..do you have a vented bov to atmosphere? has it been adjusted properly? is it sealed properly to the ic piping...

with no codes and the symptom you are talking about i would go through all your IC piping and couplers to check for leaks.

 

[Nomad707]

maybee your Intake manifold / throttlebody gasket is leaking? this could cause idle fluxuations and roughness.

happened to me, replaced gasket and she puurrrs

 

[smagnotta]

Yeah I switched back from the +30% correction to -3%; I have a wideband O2 sensor that can help me with the air/fuel correction.

IdealSupra thanks for the ECU -- it ruled out that problem and the car seems to run better. I have the HKS SSQ BOV and it is welded directly onto the intercooler piping to the intake.

I used to have a loud backfire problem in between gears but that is now gone. Just this popping, misfiring at idle and slight surge of RPMs. When the car surges, I lose vacuum pressure and it fluctuates from -20 to -16.

 

[suprahooked]

It sounds like a vacuum leak or boost leak. It maybe a intake gasket. Good Luck

 

[Idealsupra]

well if that hks bov is vented to atmosphere....when you accelerate and let off thats why it dies...it richens itself to death because it is expecting air that isnt there because the bov released it. that could be that issue.

surging issue could be a bad iacv or maybe just a stuck one...take it apart and clean out the valve and spring with some brake cleaner. it couldnt hurt.

 

[smagnotta]

I have a brand new throttle body and TPS coming at the end of this week/early next week. The ISC on the car is also brand new. I am going to replace the throttle/TPS and inspect the ISC/clean if needed. The surging on idle should be the ISC valve. The ISC is working because when I unplug it, it surges wildly and when plugged and I shut off the car it does click 3 or 4 times. I'll check it with a multimeter.

I have the BOV welded on the intercooler pipe and then I have a vacuum line going from it back into the intake near the 3000 pipe. Yes, I am not recirculating and it is being vented to the atmosphere.

I found out from an HKS associate that it is OK to adjust the BOV with the screw if you experience a stumble on idle but it is not recommended:

"Do not touch the nut on the back of the valve ! (I wish we never put that on there ! ) Adjusting that nut does NOT change the opening rate, efficiency or timing of the valve. HKS valves are "pull-type" valves, meaning they have to "pull" open against the boost for them to open. The more boost you run, the more the boost pushes them closed. Some vehicles have more vacuum than others. If high enough, it is possible for a vehicle's vacuum at idle to accidentally pull the valve open, causing a vacuum leak. It is for this reason that HKS employees an adjustment nut on the back of the valve to allow the spring tension to be adjusted, ensuring that the valve is closed and not leaking while the vehicle is idling. If you have played with this nut, I would suggest getting it back to the middle adjusting point while being VERY careful NOT to let the nut fall out, or turn it too tight as to puncture a hole in the blow -off valve diaphragm. As long as it's not leaking at idle, you're fine."

 

[sneakypete]

i had the same problem a few years ago and after all the headaches and hassles of finding some serious problems.. it ended up being something so easy.
it turned out that the rubber air hose that goes from the accordian hose to that metal pipe thing to the isc was cracked where it was being clamped down.... so i just replaced the whole thing with a new rubber hose that eliminated that metal piping.
i feel that the more connections you have (with clamps or welds etc) the more likely you are to get a leak.
so try checking all those old rubber hoses by the intake. they seem to rot faster since they are right near the turbo.
-pete