High Idle - Newbie Needs Help

[onslow]

Hi Guys-

After Spring cleaning and tuning, my numbers in Park (closed loop) are good (OTC scanner):

BLM - 131
MAF - 6
IAC - 14
TPS - 42

However, the idle varies 975 - 1050 RPM which seems at least 125 RPM too high according to posts I have read here. Car idles fairly smooth and runs well.

I have played around with various combos of IAC and TPS but the best I could get was 950 - 1000 RPM.

I would appreciate any helpful ideas you might have or any other info you need from me. I will be taking car in for TEST only smog (California) and want to ace the test.

If you think the issue may be the chip or ECM (both original stock), how can I tell which one is bad (I do not have access to an oscilloscope)?

Only one other thing might be relevant...after 7 mile test drive, shut it off and immediately tried restart...it would not start. I unplugged and replugged ECM power and it started.

Thanks,

Steve
onslow@myway.com

'86 T-type; Walbro 340M, Racetronix hotwire, Kenne Bell dual exhaust, valve cover breathers, AC R43-TS plugs, new IAC, crank sensor, coil pack, ICM.

 

[gnmike87]

IAC seems a little low. It has to be adjusted with the tps. It seems like always shot for 30-40 IAC.

 

[oddfire6]

check for vacuum leaks. you should replace all the vacuum lines if any are in doubt. after almost 20 years they tend to crack....

 

[SFITurbo]

I use Winaldl to tune, plugging into ADL causes idle to raise,(diagnostic) but lowers after unplugging. I usually see those numbers also.

 

[onslow]

Thank you one and all.

I think it might be scanner plugged into ALDL...I read a post about this happening, and I notice RPM is lower when tool is not plugged in.

So, if this is the reason for the high idle, how can we get a good RPM reading with scan tools like Winaldl or OTC?

No vacuum leaks I can detect (WE-40 method), and I replaced all vacuum lines recently.

I may go a little higher on IAC if I can keep idle smooth.

Any ideas why car would not start, but did after unplug/replug of ECM's power?

Thanks.

Steve

 

[2QUIK6]

Actually, the numbers are perfect. IAC you want below 50 but every car I've seen likes them to be below 20 at idle but at least >10. As long as its not hitting 0 you're fine..when it hits 0 means it can no longer control the idle speed. The idle speed is programed in the chip in the ECM. If the IAC is not changing steps, then the commanded idle speed is met at 14...if the idle speed was lower then the IAC steps would reduce even further down to 0...in the case of a vacuum leak.. Also if you had a vacuum leak, the BLMs would be way higher than 131, like >140.
AS far as the dying..not sure unless its the fuel pump relay, but cutting the car off and letting it sit about 20-30secs and turning the key back on should have had the same effect as unplugging the ECM.

In that situation, be sure you hear the fuel pump energize when you turn the key to the "on" position without starting. A fuel pressure gauge may come in handy too.
Just this w/e I went and looked at a GN that was for sale...and it would not start. Owner didn't know what to do so I poped the schraeder value cap off and discovered there was no fuel in the rail. Grabbed a wire and jumpered a connection from the "+" battery to the empty brown plug/connection behind the altenator...after a few touches of the wire, the pump fired up and then the car started right up..think the fp was just stuck a little from sitting or something..started right up every time after that.

 

[Brian Mc]

the scanner needs to be in road test mode, not field service. You can switch it, it tells how in the manual; I had the same issue.

 

[onslow]

Thanks Brian...I have been ignoring my own "to do" note to put the OTC in road test mode for three weeks! I think that qualifies me as an ASE certified idiot as well. I will change my behavior immediately.

Steve