hosrom_951

Car starts up (bit slow, cranks but some time needed to start), then some exhaust popping (but no cat or muffler). So, driving normally on the highway, come to a stop. Everything is fine, then drive along, come to another stop, THEM i noticed that the rpm reads 800! and it feels like it's going to switch off. But stays there, then goes up to 900, stays there for a while, then drops back to 800. At 800, you can JUST feel some stumbling, but when revved up, everything is fine. ALL vacuum pipes are new, but i was suspecting 2 things before this started to happen. 1, the throttle position switch is faulty, due to at half throttle some cutting action (not so noticable) and 2, a fuel pressure regulator. I tried playing the the idle valve, and the car revvs up (reaching 1,000 rpm) and tried to close it a bit, making it reach 800~900rpm. But i noticed something, a hissing noise coming from the AFM,everytime i open the valve, the hissing noise comes louder, i know that that is air coming into the system, but is that normal? maybe the valve is stuck and i need some grease on it?

Danno

That 800rpm is actually closer to 600rpm due to the tach being a little off at low-RPms. Don't try to force a 800-900rpm idle, it should be just a tick over 1000rpm on the tach.

Jim @ EuroWerks

I notice al 951s have that hissing noise at the AFM (normal). After you look at 5 to ten of them for a leak in this area including the hose under the throttle you figure they all make the sound. And everyone I ck does. Sounds like the boot, but it's not. Do ck the throttle switch if the control unit doesn't get the idle signal the ICV will not operate correctly. Danno, who's the hot babe rubbing here *** on the car?

Jeremy Himsel

Are you sure about this one? On both my 951's the stock tach is pretty close. On my primary car it is when measured against my AVCR and smt-6. On my other one it's pretty close to an autometer tach.

hosrom_951

Well, after driving around last night after the car sat for 4 hours. Everything was fine. 26 mins of driving no problems. Then it started again, After listening closely to the way the engine stumbles and sounds, and the decrease in fuel milage ( i used to get around 550~650kms in a full tank, now i get 450~550kms). I suspect the fuel pressure regulator, this morning, after 1/2 hour of driving, the car idles fine, but feels SLIGHTLY rough, so i am replacing the regulator this weekend.

Mike Murcia

Jeremy, I don't think the AVC-r can accurately measure the rpm due to it not having a setting for the sampling rate of the RPM sensor. It gets a signal that is used for tuning, but it is also off a bit.

Peckster

Check that the air adjustment screw hasn't fallen out of the throttle body. If the hissing stops when you put your finger on the hole, that's it. Just jam something into it until you can get a new screw.

rage2

My AVC-R is VERY accurate. I have my rev limiter set at 7000rpm on my SDS, and AVC-R reports 6994 everytime I hit it. The stock tach is far from accurate, about 100rpms too high for me at low rpms.

Sam Lin

I believe the speed sensor is what the AVCR cannot adapt to, not the RPM.

Sam

Jeremy Himsel

Mine is dead nuts. Hooked up to DME terminal 1. The speedo is what's inaccurate. Without proper RPM signal, It wouldn't be worth it to go with the AVCR as you couldn't use all of its options.

hosrom_951

Ok, the car idles fine now. But amazingly, fuel mileage decreases and more pops in the exhaust, that is definitely the fuel pressure regulator right?

Danno

"I notice al 951s have that hissing noise at the AFM (normal). After you look at 5 to ten of them for a leak in this area including the hose under the throttle you figure they all make the sound. And everyone I ck does. Sounds like the boot, but it's not. "

Yeah, I think the hissing noise is the bypass passage that vents air around the flapper door. This bypass-passage is adjustable (like the throttle-plate bypass) and is used for the HC/CO adjustment. More air going around the flapper-door without being measured gives you a leaner HC reading. Less air being bypassed gives richer HC at idle. DO NOT crack open the AFM and adjust the spring-tension in order to adjust idle-mixtures, it'll mess up your air-fuel ratios across the board.

"Do ck the throttle switch if the control unit doesn't get the idle signal the ICV will not operate correctly."

Also, check your vacuum level at the FPR. Normal idle-vacuum should pull down the fuel-pressure from 38psi to about 30psi. Same thing under steady-state cruising on the freeway. If you're not reducing fuel-pressure when the car's operating under vacuum, you'll end up with a too-rich mixture and bad gas-mileage. The pops in the exhaust are a sign of this too-rich mixture.

"Danno, who's the hot babe rubbing here *** on the car?"

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