Idle problems and I'm at a loss

[BlueRB240]

Ok here is the problem, I can't seem to get my car to idle unless I pull the big vacuum line off that goes to the break booster. If I leave it on and try to start the car it just won't turn over. The air fuel ratio while it's cranking with no vacuum leak is like 10ish, with it off it's around 14ish and when it fires up it's at 16ish. So when I fire it up with the vacuum leak that car will ilde high but it will stay running until I seal up the leak then the airfuel ratio shoots to the 10's and the car stalls out. I tried to unplug the maf to get it to idle and it just won't do it. Checked the ecu for codes but none all is good. I thought maybe my injectors were dirty and they were a little from the report I got back after I had them cleaned and balanced. I'm running 824cc Sard injectors with a Nistune Ecu and Denso 280lph fuel pump. I also reprogrammed my nistune and tried it another Rb20 and that car fired up like normal. I'm at a very big loss because I have never seen this before.

[Matt]

The reason why your AFRs are going richer with the vacuum line connected is because the MAF is measuring more air and then injecting more fuel consequently

If you change your injection multiplier to compensate for the extra richness then the car should idle/run accordingly

[BlueRB240]

I tried to adjust it and plug it back in but same result it would just die. The strange thing was it ran before but now it just started to act up.

[Matt]

hows your AFM voltage reading?

[BlueRB240]

something happened to my log. I'm going back to the shop tomorrow I'll get a log of it trying to start with the no vacuum leak and with the leak.

[BlueRB240]

Ok got a chance to go back up and make a quick log. I pulled the Vacuum line on intake manifold to get the car to start. The idle is high because I was messing around with the idle control screw last time. There is a part of the log where the idle gets a little lower. I pulled the hose that goes from the Idle air control valve to the other valve which the name escapes me at the moment. When I pulled that hose I sealed up the leak that I made to start the car. Then at the very end of the log I sealed everything up while the car was running and it stalled out.

[BlueRB240]

.....bump........

[PL]

You don't just have a dodgy AAC valve do you? Which would stop the engine from getting enough air to support idle. By bleeding extra air (albeit unmetered) into the manifold the engine would then get enough air to support idle.

AAC valves are something that can tend to go faulty on older engines.

PL

[BlueRB240]

You don't just have a dodgy AAC valve do you? Which would stop the engine from getting enough air to support idle. By bleeding extra air (albeit unmetered) into the manifold the engine would then get enough air to support idle.

AAC valves are something that can tend to go faulty on older engines.

PL

well I bypassed the AAC valve since it's on the top of my rips manifold and the car still died. Unless I have the plumbing all wrong?


There is a vacuum port under the intake manifold where a hose goes to the front of the AAC valve then to the IAC where it T's to the valve and to the intercooler piping. My next trip up I'm going to pull the intake manifold off and clean the IAC since I'm all out of idea's lol.

[PL]

Whoa - nice manifold!

The other thing you could try is just cracking the throttle a bit (adjust it) but you may need to fiddle your TPS adjustment to keep the "TPS Closed" flag active or it won't idle properly.

Although RB20 has a separate switch for that doesn't it? Sorry - I'm SR boy so I'm not that familiar with the intricacies of the RB intake.

But the bottom line is that if this is something that happened recently then there's a problem that needs sorting. Don't try to tune around it.

PL

[BlueRB240]

Ok I think I got it now. I built a boost leak tester and found a few leaks but they weren't anything crazy. So I test a different Ignitor, borrowed my friends RB25 coil pack and same thing. I changed the IAC solenoid and cleaned out the body. Still the same thing ran really rich and started to foul out my plugs and idle like crap. So I decided to play with the Injector Multiplier while I held the revs on the motor to keep it from stalling out. I watch the A/F ratio which was at 10.1 start to go up the more I lowered the value it had of 200 till I got to 86 and it was very close to the A/F in the cell. Played with it some more till it was smooth to rev and now it idles fine! arg wait a pain.

[TM_S13]

so you adjusted the K constant is that it ?

if so... it seems like the injector resizing wasn't successfull... have you done it by the way ?

[BlueRB240]

Yeah the K constant. I tried the Resize from the pull down menu but it didn't work. I thought it worked at the time so I was looking more mechanical side of the things.

[TM_S13]

I'm not sure about this.. but... it might be due to some latency values differences between the stock injectors and sard injectors...
it's weird though...

[PL]

The injector re-size facility is really just a semi-automated way of adjusting your K constant for your new injectors. It just works on a ratio of old vs new injectors. The nice part is that it also re-calculates your load scales and TTPmin/max.

But if you understand the basics of what's going on you can do all this stuff by hand very easily anyway.

Running large injectors (I see anything over 740cc as large) makes everything harder, so you may have to put in some time to get everything in place. And with 824's you'll almost certainly need to play around with injector latency to get things working nicely.

I always recommend that for your first tune you stick with basics. Huge injectors and modified everything is never gonna be easy. But I understand that it's not always possible to dip a toe in the water first and a big splash into the deep end certainly makes you learn fast!

PL