bjohn3x

Hey guys, need some advice. I have a 1999 Si, with I believe the original B16A2. Had the motor rebuilt (in chassis) about 50K ago due to a blown valve, got 166K on it now. Been reading forums and trying things for WEEKS and am going crazy. Everything I've read indicates a vacuum leak, but I can't find it. As it sits now, engine idles at ~1500 cold and is steady. As soon as the IACV activates, starts pulsing from 1100-1900rpms non-stop.

Have been having some intermittent idle issues over the past 2 years, but have just ignored it. random high and low, then dying at a stop. Nothing to keep me from driving it. Then it started the pulsing at PT and idling at about 1500rpm and bogging hard on decel. There was another post EXACTLY like mine, he tried everything...then eventually replaced the entire intake -> to the TB and the problem was fixed. Not the solution I was looking for.

Things I have done:

1. Checked for coolant air bubble
2. Found TPS was out of adjustment, adjusted to .485v at idle and 4.5 at WOT
3. Adjusted throttle cable
4. replaced IACV (don't think the old one was bad)
5. Replaced ECU with other used one. Same result
6. Used brake-clean and sprayed all around the intake gasket, TB gasket, hoses, IACV gasket, injectors...no change in idle.
7. Cleaned TB, Sea-foamed through brake booster line.
8. replaced TB gasket
9. 50k old OEM PCV valve tests good.
10. Verified the cruise vacuum line was not disconnected.

What's next? I have an OBDII reader. only code is P0505. Thank you in advance for your help!!!

tony_2018

smoke test...if it is indeed a vac leak you'll find it there.

bjohn3x

Ever done that from home? Any DIY for that test? I don't have a smoke machine. Thanks for the reply!

tony_2018

Check youtube, might find some homemade diy smoke testers. Will do the job without breaking the bank.

Former User

Test the ECT sensor.

bjohn3x

Ok cool, will try one out and post the results.

Former User

Ohm test it with engine fully warmed up. Or use a scan tool.

bjohn3x

Please explain what IT is and what results I should see when OHMing it out. Thanks!

Former User

ECT sensor

200-400 Ohms = spec

bjohn3x

Ah ok. I'll do that, but my scan tool seems to be reading the correct temp. About 200deg when warm....but I'll double check. Thx!!

Former User

What's the temp reading when the engine is cold?

Does temp reading fluctuate when idle is surging?

What are the TPS reading with the scan tool?

bjohn3x

Temp reading when cold is 73deg. After recent adjustment of the TPS, 8.2 at idle and 87.5 at WOT. Just warmed up the car. it's only 50deg outside so it only got to 180deg. I let off the gas and it was doing the hunting for 20sec, then the CEL came on. As soon as it did, the idle went from hunting to a fast pulsing around 1600rpm.

The temp reading did not fluctuate. I have a bucket with a lid, now I just need some tubing and a few cigars for the smoke test. Anything else I can try for you guys in the meantime?

Former User

Remove the air intake. Run engine until you get the high idle or surging idle. Use you finger to cover hole inside TB leading to IACV. Does idle speed drop and steady?

bjohn3x

Yes it drops and stabilizes

Former User

Rules out a vacuum or intake air leak, and means the problem likely lies with the IACV, ECT, or TPS.

Have you tried adjusting the idle speed as per service manual?

bjohn3x

Actually, not since I fixed/adjusted the TPS. Lemme walk through it.

Former User

You need a tachometer more accurate than the one in the cluster, so use your scan tool to read engine rpm.

rollinmyda

iTrader: (19)

Your TPS is out of spec. The ecu will try to compensate using the IACV but when it's unable it will throw a code P0505. Go through the TPS calibration procedure using the fsm again.

bjohn3x

Oh? I calibrated it to 4.5v at WOT and then adjusted the throttle plate stop screw to adjust the idle voltage. My voltages are in spec, why do you say its out of cal? What's FSM?

bjohn3x

I cannot do the idle re-calibrate because with everything unplugged and the idle screw all the way in, it's still at 1500 rpm. so clearly something else wrong

bjohn3x

Factory Service Manual? I can google.

Former User

What happens to idle speed with IACV unplugged?

Former User

This^ is almost surely the problem. Never touch the stop screw.





Calibrate the close throttle voltage first (0.5V) and then just check the WOT voltage, which should be ~4.5V.

bjohn3x

if I clear the CEL, fire it up when warm it'll hunt from 1k - 2k. If I go unplug the IACV it starts the 1500-1700rpm fast pulsing.

rollinmyda

iTrader: (19)

FSM= Factory Service Manual

Do you have one? I don't have my laptop with my copy of the FSM with me so I can't check what it gives as a spec for that engine but I believe it should be .50 volts at idle (throttle plate fully closed). You mentioned in your OP that you adjusted it to .485 volts and then mentioned the scan tool is reading 8.2 volts at idle.

Why did you adjust the throttle stop on the throttle body? I would never recommend doing that. What that will change is the overall range of movement of the throttle plate and isn't intended to be used to make minor voltage alterations to the TPS. To adjust the TPS you should be using the two screws that affix it to the throttle body and I would recommend adjusting the idle (fully closed) voltage first, not try to adjust the WOT voltage.

Ron beat me to it... lol