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98 Trooper fast idle and stumble?

Tiny
MRTRDRVR
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  • 1998 CHEVROLET TRUCK
Hi and thanks in advance for your help.
I have a 98 Isuzu Trooper 3.5 with 98500 miles.
I replaced the rings, rod and main bearings, crankshaft, timing belt and idler pulleys. New TPS, and MAF sensors. I also replaced the Idle air control with a used unit off a 91 chevy beretta. Since replacing the IAC, when you first start the engine it immediately goes to 2000 rpms then after about 20 seconds it drops gradually to 830. Outside temp is about 30 degrees. Are all IAC's that look the same created equal?
Also when I drive it gently it runs great, but if you floor it it seems like it misses and the check engine light comes on immediatly and starts blinking. I pulled the spark plugs and though they were newly installed they are velvety and black.
I haven't driven it since replacing the MAF sensor.
Thanks Dale
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Tuesday, March 6th, 2007 AT 7:25 PM

8 Replies

Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
I would use one for the correct application. Is the cam timing correct? If the crank is retarded even though the cams are timed properly to each other it will have low power and thus the compression will be lower causing the rich condition.
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Wednesday, March 7th, 2007 AT 7:43 AM
Tiny
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I just got back from driving her. When using only low power everything seems like it runs fine. At a steady constant 55 mph there is a flutter? Vibration? That goes away if I add a little throttle. If I give it 80% to 100% throttle it begins to cut out and gets worse the harder you push it, on the floor it's like someone is turning the key on and off.
The high idle problem seems to be getting better it doesn't rev as high or stay up as long.
Compression for cylinder 1-195 2-195 3-215 4-205
5-215 6-205 for 5 revolutions.
Thanks again, Dale
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Wednesday, March 7th, 2007 AT 7:30 PM
Tiny
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Ok, I found out what was causing the surge, miss, whatever. It turns out my number 4 cylinder injector lower o-ring was allowing a small amount of air past. Put new ones on and no more cutting out.
Now I took it out again and ran her pretty hard and the cel came back on (so I backed out of it) and blinked a couple of times then stayed on steady. I scanned it and it comes back " P0300 Random/Multiple Cylinder Misfire Detected ".
What's causing that?
No spark plug wires, it's coil on plug. New plugs. The connections are clean dry tight to the best of my ability.
When I changed the injector o-rings I pulled the vacuum line off the fuel inj pressure regulator and a couple drops of gas made it's way out.
Do I need a new one? Would that cause the po300?
Thanks again, Dale
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Thursday, March 8th, 2007 AT 8:57 PM
Tiny
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Ok, apparently this site doesn't want you mention part store names.
After doing some more reading I've ordered a new idle air control, fuel injection pressure regulator, and both front oxygen sensors. Hopefully that will cure it running rich and turning on the CEL.
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Saturday, March 17th, 2007 AT 11:30 AM
Tiny
RODEO93TPS
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Dont you just love misfires? :X fast idle I have heard means a bad o2 sensor but it could also be a problem in your vac system check for leaks I had a tiny little hose come off in my engine and the entire thing ran poorly until I fixed it. Might not be the case for you but it can't hurt to try :|
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Friday, March 23rd, 2007 AT 8:46 AM
Tiny
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Thanks for the response, I actually went over the hoses and sprayed them with carb cleaner listening for the engine to change idle. That is how I found the injector o-ring leaking. Between both oxy sensors and replacing the Idle air control I hope the idle prob will be taken care of. If not, I 'm at my wits end.
Dale
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Friday, March 23rd, 2007 AT 9:23 AM
Tiny
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Well I installed the correct IAC and did it the correct way (boy directions sure are nice) and it idles fine now.
Installed the fuel pressure regulator and both front O2 sensors and she still turns on the CEL when applying 90% throttle or more.
I scanned her and it came back PO300 multiple
cylinder misfire again/still.
And just to throw in some nonsense it also added that the voltage on my MAF was to low or to high. I just replaced that so now what?
Any idea's?
Dale
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Monday, May 7th, 2007 AT 11:09 PM
Tiny
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Well for those interested in my continuing saga, it turns out that the MAF sensor I had installed was bad and I needed to replace it.
After replacing with another remanufactured unit no more check engine light and it doesn't stall while idling and gets better gas mileage. The fuel trim numbers are a lot better now since the engine doesn't have to guess at the amount of air it's using.
Dale
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Thursday, August 9th, 2007 AT 8:44 AM

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