Hesitation cured Thanx PontiacX2
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Joined: Jun 2001
Posts: 29
From: Grants Pass, OR, USA
Hesitation cured Thanx PontiacX2
After reading the post by PontiacX2 I decided to try a new IAT sensor ($10.99) Autozone. Low speed hesitation/stumble is gone.
Engine also is running cooler. I have chased this problem for a long time. The IAT tested good, it was one of the first things I checked. Problem showed up after the opti got wet, thought replacing it would cure the problem. I have changed the opti, coil, coolant temp sensor, plugs, wires, map sensor, fuel filter, TPS. Didnt have to replace the MAF, its a 93, doesnt have one. Tried new injectors, anybody need some Bosch purple tops? Checked wiring, voltages, etc. Bypassed the knock sensor, blocked the EGR, gutted the cat, TBB, relocated the coil and ICM. Had it scanned by a chevy dealer, a waste of money, they thought maybe a blown head gasket, this without a compression test, WTF. The new injectors helped for awhile, ran pretty rich, gradually the closed loop stumble returned. Went back to the stock injectors and installed a manual fan switch, keeping it cool minimized the stumble.
With the new IAT, no stumble, even at 190 deg. Engine is staying about 20 deg cooler. The IAT I replaced tested good twice. If you have the low speed stumble this is a cheap thing to try.
93 M6 RED 59K
Off road pipe, B&M Shifter, EGR, TBB.
Engine also is running cooler. I have chased this problem for a long time. The IAT tested good, it was one of the first things I checked. Problem showed up after the opti got wet, thought replacing it would cure the problem. I have changed the opti, coil, coolant temp sensor, plugs, wires, map sensor, fuel filter, TPS. Didnt have to replace the MAF, its a 93, doesnt have one. Tried new injectors, anybody need some Bosch purple tops? Checked wiring, voltages, etc. Bypassed the knock sensor, blocked the EGR, gutted the cat, TBB, relocated the coil and ICM. Had it scanned by a chevy dealer, a waste of money, they thought maybe a blown head gasket, this without a compression test, WTF. The new injectors helped for awhile, ran pretty rich, gradually the closed loop stumble returned. Went back to the stock injectors and installed a manual fan switch, keeping it cool minimized the stumble.
With the new IAT, no stumble, even at 190 deg. Engine is staying about 20 deg cooler. The IAT I replaced tested good twice. If you have the low speed stumble this is a cheap thing to try.
93 M6 RED 59K
Off road pipe, B&M Shifter, EGR, TBB.
Registered User
Joined: Aug 2002
Posts: 2,325
From: BC
Would be interresting to get someone to send one of the IAT sensors to someone with a scanner so that they can read what's causing the stumble to happen... Being a computer guy, i've learn't that although sometimes things seem to happen for no reason at all .. theres ALWAYS something causing it. How'd you test it Seabat? Glad you solved it!
Registered User
Joined: Mar 2002
Posts: 4,827
From: Waynesboro, PA
Seabat:
What was your stumble like? I have a low rpm stumble that only presents itself when I do a quick roll into Wide Open Throttle. It will fall on it's face for a split second, then pick right back up. It doesnt happen over about 2500 rpm, and I really hate to think that a brand new Opti is going out.
What was your stumble like? I have a low rpm stumble that only presents itself when I do a quick roll into Wide Open Throttle. It will fall on it's face for a split second, then pick right back up. It doesnt happen over about 2500 rpm, and I really hate to think that a brand new Opti is going out.
Thread Starter
Registered User
Joined: Jun 2001
Posts: 29
From: Grants Pass, OR, USA
Details on IAT and hesitation.
I checked voltage at IAT several times. Checked IAT resistance versus temperature, had a chart with values, cant find it now. Was checked when I had car scanned, for what that was worth.
Had the classic low speed stumble, ran fine when cool, once it was warmed up it was dead below 2000 rpm. After 2000 it ran fine. Tried it with O2 sensors disconnected to keep it in open loop, still had the problem.
The most interesting thing is that it is running cooler with the new IAT, the exhaust tips are starting to lose the coal black soot from running rich. It would appear to me that it has leaned out a bit and the spark is advanced to some degree. I pulls well from idle on up through RPMs.
If the stumble comes back I will try another IAT sensor, if that fixes it I will start checking voltages in and out of the IAT while driving it.
93 M6 RED 59K
Off Road Pipe, EGR, TBB, B&M Shifter
Had the classic low speed stumble, ran fine when cool, once it was warmed up it was dead below 2000 rpm. After 2000 it ran fine. Tried it with O2 sensors disconnected to keep it in open loop, still had the problem.
The most interesting thing is that it is running cooler with the new IAT, the exhaust tips are starting to lose the coal black soot from running rich. It would appear to me that it has leaned out a bit and the spark is advanced to some degree. I pulls well from idle on up through RPMs.
If the stumble comes back I will try another IAT sensor, if that fixes it I will start checking voltages in and out of the IAT while driving it.
93 M6 RED 59K
Off Road Pipe, EGR, TBB, B&M Shifter
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