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engine rpm surge. help needed.
#48
the ECU never shuts the ISC closed 100% (unless massive air leaks are happening) it does in fact run 50% and is the 50% idle dutycycle rule. (the bleed screw is that calibration POINT)
the FSM covers this but what you do is. (in a nut shell ) and need tool to measure duty cycle, as most do not. Ill cover this 2 ways. (a man with tools or not)
1: end all illegal vacuum leaks (air) find them end them.
2: engine hot. 150f , 180f , 195 f (195F thermostats work best in cold climates) 150f is the IAC calibration point set at the factory and what the ECU expects to see !!!
2b: a/c off, (on 1989/90 more things must be off , ask) we are doing 1992 + 16v only here.
2c: steering pressure switch not closed, (or wire shorted there causing 1000 RPM. fast idle mode, to be in effect, fix this next and a/c errors,for same.
3: make sure iSC unplugged, idle drops well below 800 rpm, if not close the bleed down. if you can not attain below 800 now, see #1 again. or pinch the isc air line next !
4: using the duty meter, tune the bleed screw until 50% duty is reached as seen here.
we set the bleed on a scope (1 tool example there are many tools to do this) set the bleed until the high time equals the low time. 2.5mS high and 2.5mS low, even Steven.
http://www.fixkick.com/IDLE-AIR/iac-wave1w.jpg
5: done.

with no tools, turn the bleed closed CW, until the ECU grabs RPM from you and hits 800 (+-50rpm) that is called ECU idle regulation now working
then close the bleed 2 more turns for luck,(we all this by seaman's eye, or guessing) if regulation fails at other times, close it more. until 800 is hit again.
many quality DMM meters today have duty mode, on the dial , a good idea that. it reads out in %


finding a leak is not too hard, sure daunting.
if the IAC is not leaking hot,
then its a simple gasket leak some where.
1: brake diaphragm booster (block the hose with cork, dont drive just test)
2: all hoses.
3: all induction gaskets in the whole plenum and injector cushion gaskets sucking air.
4: all vacuum operated diagrams are suspect , booster, FPR, VSV valve broken or stuck open.
some cars this old have all 4 bad, some do, expect it and win. (we test and prove other wise ) or even get a smoke machine to find it , watch you tube on engine vacuum smoke machines.
my bud uses a cigar to do that.... wow. flash light in hand look, and looking for leaks.
http://www.fixkick.com
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Messages In This Thread
engine rpm surge. help needed. - by Rapom - 12-05-2017, 02:08 PM
RE: engine rpm surge. help needed. - by Rapom - 12-05-2017, 03:01 PM
RE: engine rpm surge. help needed. - by fixkick - 12-05-2017, 11:44 PM
RE: engine rpm surge. help needed. - by Rapom - 12-06-2017, 03:11 AM
RE: engine rpm surge. help needed. - by fixkick - 12-06-2017, 04:52 AM
RE: engine rpm surge. help needed. - by fixkick - 12-06-2017, 04:56 AM
RE: engine rpm surge. help needed. - by Rapom - 12-06-2017, 05:39 AM
RE: engine rpm surge. help needed. - by Rapom - 12-06-2017, 11:43 AM
RE: engine rpm surge. help needed. - by fixkick - 12-07-2017, 01:37 AM
RE: engine rpm surge. help needed. - by fixkick - 12-07-2017, 01:58 AM
RE: engine rpm surge. help needed. - by fixkick - 12-07-2017, 02:02 AM
RE: engine rpm surge. help needed. - by fixkick - 12-07-2017, 02:48 AM
RE: engine rpm surge. help needed. - by fixkick - 12-07-2017, 03:06 AM
RE: engine rpm surge. help needed. - by Rapom - 12-07-2017, 04:41 AM
RE: engine rpm surge. help needed. - by Rapom - 12-07-2017, 02:05 PM
RE: engine rpm surge. help needed. - by fixkick - 12-07-2017, 10:34 PM
RE: engine rpm surge. help needed. - by fixkick - 12-07-2017, 10:36 PM
RE: engine rpm surge. help needed. - by Rapom - 12-08-2017, 12:21 PM
RE: engine rpm surge. help needed. - by fixkick - 12-08-2017, 11:26 PM
RE: engine rpm surge. help needed. - by fixkick - 12-08-2017, 11:35 PM
RE: engine rpm surge. help needed. - by fixkick - 12-08-2017, 11:37 PM
RE: engine rpm surge. help needed. - by Rapom - 12-09-2017, 12:57 PM
RE: engine rpm surge. help needed. - by fixkick - 12-12-2017, 12:05 AM
RE: engine rpm surge. help needed. - by fixkick - 12-12-2017, 12:15 AM
RE: engine rpm surge. help needed. - by Rapom - 12-12-2017, 01:58 AM
RE: engine rpm surge. help needed. - by fixkick - 12-12-2017, 03:48 AM
RE: engine rpm surge. help needed. - by fixkick - 12-12-2017, 03:49 AM
RE: engine rpm surge. help needed. - by Rapom - 12-14-2017, 12:46 PM
RE: engine rpm surge. help needed. - by Rapom - 12-14-2017, 01:00 PM
RE: engine rpm surge. help needed. - by fixkick - 12-14-2017, 08:42 PM
RE: engine rpm surge. help needed. - by fixkick - 12-14-2017, 08:54 PM
RE: engine rpm surge. help needed. - by Rapom - 12-15-2017, 04:35 AM
RE: engine rpm surge. help needed. - by fixkick - 12-21-2017, 04:05 AM
RE: engine rpm surge. help needed. - by Rapom - 12-17-2017, 01:10 PM
RE: engine rpm surge. help needed. - by fixkick - 12-21-2017, 04:19 AM
RE: engine rpm surge. help needed. - by fixkick - 12-21-2017, 05:55 AM
RE: engine rpm surge. help needed. - by Rapom - 12-22-2017, 02:54 PM
RE: engine rpm surge. help needed. - by Rapom - 12-22-2017, 03:36 PM
RE: engine rpm surge. help needed. - by fixkick - 12-29-2017, 04:00 AM
RE: engine rpm surge. help needed. - by fixkick - 12-29-2017, 04:02 AM
RE: engine rpm surge. help needed. - by fixkick - 12-29-2017, 04:35 AM
RE: engine rpm surge. help needed. - by fixkick - 12-29-2017, 04:38 AM
RE: engine rpm surge. help needed. - by Rapom - 12-30-2017, 12:39 PM
RE: engine rpm surge. help needed. - by fixkick - 01-11-2018, 07:23 AM
RE: engine rpm surge. help needed. - by Rapom - 01-16-2018, 01:26 PM
RE: engine rpm surge. help needed. - by fixkick - 01-16-2018, 10:30 PM
RE: engine rpm surge. help needed. - by fixkick - 01-16-2018, 10:50 PM
RE: engine rpm surge. help needed. - by fixkick - 01-16-2018, 11:20 PM
RE: engine rpm surge. help needed. - by fixkick - 01-16-2018, 11:29 PM

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