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Hard start, run, idle, it doesn't do anything right.

01-07-2010, 06:54 AM
I have a similar problem( hope you dont mind me posting under yous) I got a 94 Jimmy 4.3 Vortec VIN"W" and it would idle like it had a cam-and would rin crappy while accelerating up to the point to where it shifts into 2nd, then it would smooth out and run great, and if I stopped at a light I had a poping(almost like a backfire) coming out of the cherry bomb, but then sometimes after driving 70 mph for about 40 minutes and get off the highway and get to a light it would take off fine with no hesitation but after a few lights it would start again so I cleaned the IAC, EGR, had a few codes( IAT sensor, knock sensor,) I put in a new IAT, and it sit and idled great, took it for a drive and it still had a little hesitation but nothing like it was, then all of a sudden 2 days later the idle was real bad, all kinds of poping in the exhaust, almost dying, but once again when I got up around the rpm range for 2nd gear it smoothed out but when you took your foot off the gas while coating the idle would go up and down, checked codes- IAC and Knock sensor, so I replaced the IAC, took care of code but it doesnt have a smooth idle(the knock sensor is not hooked up yet, I had to find a replacemnet connector) And when starting it has to roll over a few times then starts- does this hot and cold - and I started it last night after work - I turned the key to ON- heard pump kick in- then rolled over a few times and started- turned key to off- and the pump sounded like it was running for another 5-7 seconds after motor was off- any ideas?

01-07-2010, 03:54 PM
Get your knock sensor connected first.

Have you checked fuel pressure and leakdown?

01-07-2010, 04:53 PM
no I havent tested fuel pressure, is the knock sensor that critical? I mean is it possible for it to make run like that?

01-07-2010, 05:10 PM
Do a Google ''Symptoms of a bad MAF sensor''

01-07-2010, 06:02 PM
1994 CMFI does not have a MAF sensor.

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