After installing a new computer the Iroc will idle in park/neutral but not in gear. When the car is started, it goes immediately to 600 rpm or so but doesn't do the familiar rpm spike and drop down to 900 or so at idle like it used to. AutoXray reads the tps at .9 but no trouble code is set - I know I need to check that. But the IAC never deviated from 160 steps...I'm thinking this might now be right since the IAC should control idle air (duh) - so how many steps are correct? It remains at 160 even though the first time I monitored the car it set a lean flag, and the second time is set a rich one...hmmm. thanks for any advice for my new toy...

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89 Iroc-Z LB9 TPI auto 2.73 posi:
3" Dynomax muffler, K&N filters, TB bypass, 3" pipe in place of cat, cleaned and flow-matched injectors, accel 300+ wires, cap&rotor, synthetic oil, flexlite transmission cooler, afpr, !air pump&diverter valve, kicker sound system, soon to attempt engine swap...

 

It should be like 35. 160 is way too much. And the TPS, well you know you need to fix that, it should be at about .35-.60 max.

 

Wow thanks...it's way off then. When the mech said my computer was bad he also said he adjusted the idle so it'd be easier to drive home...so maybe that's why the tps is so high. It also says desired idle rpm is 1137 but actual is like 726...looks like I've got some adjusting to do.

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89 Iroc-Z LB9 TPI auto 2.73 posi:
3" Dynomax muffler, K&N filters, TB bypass, 3" pipe in place of cat, cleaned and flow-matched injectors, accel 300+ wires, cap&rotor, synthetic oil, flexlite transmission cooler, afpr, !air pump&diverter valve, kicker sound system, soon to attempt engine swap...

 

U ROCK,

Please, tell me who the "mechanic" is, so I never stop there by accident. Adjusting the idle on a TPI is done at the PROM, not at the throttle body.

Get the TPS voltage set, then go back and fix the "mechanic's" screw-up and reset the minimum air position of the throttle plates. After that, the IAC problem should have cured itself.

HINT: Since the "mechanic" apparently tried to adjust up the idle by increasing idle air position, lower that first. By the time you get it close, the TPS voltage might be right where it should be.

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Later,
Vader
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"I'm gonna talk about some freaky sheet now..."
Adobe Acrobat Reader 4.0
KaleCo Auto Parts

 

Vader nails another one! THat sounds exactly like what your problem is!

Now, Vader, is it possible that on my 2.5 TBI daily driver the same thing has happened? (The cranking up of the idle stop screw) Although my IAC counts are at 0, and I get the "Idle Speed Error" DTC. I'm just being lazy by asking this, I plan to check it out soon!


TIA

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Working on:
'84 Z28 LG4 305 with 200,000 original miles!
Added dual elec fans.
145 MPH IROC Speedo
Building 430 HP 350
using primarily GMPP parts.
Block is in shop!

ASE Certified Master Tech

Starting to look like the Kicker poster child!

 

Actually this guy is the best. Well, the best retired so he's #2 in my town IMO. I drove it over there BARELY thinking I must've installed the distributor wrong, but in fact it was correctly installed but two plug wires somehow came off and one burned and was arcing. Added to this was a fried computer and a bad IAC, so no wonder it was tough to get it over there - but it sounded like a 454! some ***** revved his folgers at me...Well they diagnosed the bad computer and gave me a used plug wire for about 70 big ones. I'm not sure if they screwed anything up, but the car was MUCH easier to drive home and was almost normal except for needing gas at idle and that was with the tps at .9 and the IAC locked at 160...lol. Actually the main mechanic himself didn't work on it, it was one of his techs, but all in all I'm satisfied although they probably overcharged me slightly. But they've diagnosed several things for free for me in the past so I'm not upset. Thanks for the reply though, I appreciate all the good advice I can get, and although I avoid the mechanic whenever possible, I probably would have sent back a completely good autoXray and taken about another month to figure out that it was the computer that was bad if not for breaking down and shelling out the cash...oh well...

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Base: 89 Iroc-Z LB9 auto 2.73 posi
Exh: 3" Dynomax muffler, 3" Pipe in place of cat
Ign: Accel 300+ wires, cap&rotor
Fuel: Cleaned and flow-matched injectors, afpr, !air pump&diverter valve
Sound: Kicker
Suspension: KYB Shocks, BMR Strut Tower Brace
Misc: TB Bypass, Synthetic Oil, Flexlite Transmission cooler,
free mods, hopefully engine swap and 4th gen seats in the works...