Bad IAC valve? Odd idle issue.

[justin]

Been fighting this idle issue the last few days. Current symptoms, during cold start, idle bounces between ~900rpm and ~1300rpm until it warms up. Once at operating temp the idle settles nicely at around 850-900rpm. The second problem is the car stalls often on deceleration. Say I'm coming to a stop sign/light and I push in clutch and brake to stop. Well, instead of the rpms dropping down to 850rpm and idle'ing, the rpms drop low, under 500rpm. Sometimes it stalls, sometimes it catches itself and gets back up to 850/900rpm idle. I can sometimes reproduce this just sitting here in my garage at idle, and blip the throttle, it will drop real low then come back up. I took some datalogs of this is anyone wants to look.

Relevant info:
d16y8/z6 low compression ~8.8:1, new engine, ~350 miles on it.
y8 intake mani with b16 tbody
40 micron fuel filter, fuel pressure set to 38psi with pinched fpr vacuum
Hondata s300 loaded with stock p28 calibration.

What we've done:
fixed bad vacuum leak, don't think there are anymore vac' leaks cause I can plug the tbody up with my hand and engine will immediately stall
clean out iacv with carb cleaner
calibrated tps sensor per helms, ~.4v closed ~4.6v fully open I believe were the recommended.
adjusted idle screw with iacv plug still connected. If I tried to set the idle like the helms says, by unplugging iacv connector, the car just stalls. I cannot keep an idle at all without iacv plug connected.
reset timing after that
re-adjusted throttle cable

A few other things I cannot remember off top of my head but basically anything related to idle problems. I'm going to put my hondata 4bar MAP sensor on and see if it's the MAP. But not sure what else to try.

Hondata datalog:
http://jackmoves.com/~justin/warm-idle-decel-drops.s3d

Justin

[justin]

Tried other MAP sensor, same problems. (changed the hondata calibration for the new MAP sensor too).

Justin

[justin]

Ok...more work on idle issue today, same old shitty problem!!

;OwnEd;;OwnEd;;OwnEd;;OwnEd;

Here is what I did this time:

-cleaned iacv again
-cleaned out tbody, idle adjust screw and hole
-set throttle stop screw
-new air filter (old one broke)
-verified resistances were correct on TPS sensor
-verified voltages were correct on ecu harness plug for TPS fully closed and fully open (.509v closed and 4.6v open)
-set timing in hondata using "set timing" feature (to 16 btdc) and then set dizzy timing to the center mark on the 3 mark set on pulley.
-set base idle successfully this time w/out iacv plugged in, it chugged along at 500/550rpm idle
-plugged iacv back in, checked timing again to make sure it was good

Let car sit for 20 mins to settle/cool a little. Start it up, idle bounces up and down and up and down between 600rpm and 1200rpm, sometimes lower. After couple minutes it stabilizes at 850/900rpm according to hondata. Every other minute or so the idle will just drop to 200/300rpms and bog down, then idle back up normally, seemingly for no reason???

Blip throttle up to 3k rpms, the rpms come down and car nearly stalls, one time it DID stall doing this. Just sitting there in my garage.

Took it for a drive. Anytime I decelerate and push in clutch the car almost stalls, battery light flickers on/off and engine drops to 200/300rpm before catching back up to 800/900rpm. Other then this car is running strong and pulling hard (for stock low compression), I am at least happy about this.

That is where it sits...I'm friggin pissed. Oh, and turning on lights and heater full blast does nothing to idle, it stays normal @ 850/900rpm.

What could it be? These are remaining things I can think of to check/replace:
iacv
throttle body (one with stock positioned TPS)
fuel filter?? (I have one of those little "Trick" black filters, 40 micron metal cheese grater type filter)

Justin

[HONDA GHANDI]

Check the "invert Purge valve" box in the SManager software. OBD-II engines idle better when this is checked using the Hondata setup. Also play around with the idle mixture and frequency for smooth idle on cars with larger injectors and MAP sensors.

[justin]

Check the "invert Purge valve" box in the SManager software. OBD-II engines idle better when this is checked using the Hondata setup. Also play around with the idle mixture and frequency for smooth idle on cars with larger injectors and MAP sensors.

Ok I'll try the invert purge valve tomorrow. I'm still running on stock injectors/MAP at the moment though. Idle is fine except when coming to a stop and cold start situations :/ If I could get rid of the stalling issue when slowing down and cold start bouncing idle, it would be perfect.

PS: shouldn't you be sleeping!? :D

EDIT: cool just found this note too in hondata help, looks promising /crosses fingers

7. Increase the engine speed to 2500 - 3000 rpm and abruptly let off the throttle. If the engine speed dips below 850 rpm, move the duty cycle slider to the right. If the engine speed hangs above 850rpm for some time, move the duty cycle slider to left.

Justin

[justin]

FIXED!

Fix cold start idle bouncing = checked "invert purge valve" box in hondata under Misc. tab. Idle'd fine on cold start then.

Fix stall issue when bringing rpms up then letting off = adjusting iacv duty cycle in hondata to the right. Blip throttle up to 3k and it holds idle rpm when it comes down now just fine!

I still need to road test but this is much much better so far. Thanks for the tips Tobi!

Justin

[mavvrik]

This is just my .02 but I had a friend who had your exact same setup, same motor and ECU, and he had to have his S300 finely tuned or else his idle would be all messed up. The closest thing we could get to on colaberations (if we lost his custom shop tine) was the stock p28 tune. However, when we would run that sometimes we could get it to start up and than it would die in less than a minute, or it wouldn't even start at all. Or even sometimes we could get the p28 tuned to a point where we could get the car running but it would red line about 2000rpms early.
My point after all this is to check to stock p28 tune. Make sure that your motor likes it because I can say from personal experience that sometimes that "setup" doesn't work right and mess up your car and cause idle issues.

[justin]

Thanks for the info. The car has been running great all along (when driving), other then these 2 idle issues (cold start bounce, decel' stall). But it seems they are fixed after doing what Tobi and the Hondata help manual said about setting idle.

Once I'm done with lunch it will be test drive time.

Justin

[justin]

Road test survey results: Great success!

Idle's like a normal Honda now! Thanks for the help.

Justin

[HONDA GHANDI]

Good news. Moral of the story: basemaps are basemaps, tuning required. I can get almost every setup to run perfectly with the right tune, it just takes patience and a working knowledge of the system and all the parts involved.

[justin]

Yea, I would have never have thought to check idle issues in hondata. After driving it a few days it's going good, still the random hiccup in idle. Sitting at a light or stop, idle will drop for just a second to 500rpm or so then go back to normal. Nowhere near close to stalling though anymore, in any situation.

Probably needs some more fine tuning, but I don't like to carry my macbook pro in my car all the time :p Plus, the 1000cc injectors going in soon anyways, I'll save the fine tuning for then and when it's on your dyno for the tune :p

Justin