rough ilde at start up

[beretta]

So my 96 z26 has always had a rough idle at start up but normally leveled out within a few seconds and was fine. now that the weather is getting colder seems to be more temperamental.

I have recently had the odd code on the scanner of cam position sensor.

I changed the cam sensor the other day while i was changing my power steering pump, its not brand new, but i removed it from a 3100 block that had 0 miles. an suv was donated to the school and was tore apart, i have the block with pistons/lifters/cam/rockers. but no crank

Got home cleared the codes. SES light has not come back on in 3 days yet. but still has rough idle when cold started.

When i start it, it start and the rpm jumps from 800 down to like 200 back and forth and stalls out. i have to hold the throttle just a little for probably 60 seconds and slowly take my foot off the throttle and it will level out and idle, once it warms up i can shut it off and starts fine all day long. if i plug the scanner in and watch miss fire counts when i cold start it shows constant miss fires all across but soon as its leveled out the counts clear and no SES light ever comes on from this.

Today i changed the coil module and no difference. i have also changed the idle control valve a while back with no change.

I have a 3100. with 3400 throttle body and cold air intake ( true cold air) the tubes run down through the existing air box hole and my air filter is inside the fender. all sensors are hooked up.

I have played with just about everything i could think of, even messed around with the fuel pressure regulator.

Could i have a bad injector ? why would it only cause issues at start up.

Car runs fine once it warms up for a few seconds and is fine all day, still hauls butt. no performance loss at all, i have put injector cleaner through it a few times over the summer, and more recently started putting gas line antifreeze in every fill up and nothing makes any difference.

Im going to try plugging in the block heater tonight to see how it starts in the morning.

[2.2H8TA]

I have almost the same problem, just not as bad. I've never had any codes however. I think mines problem is injectors, I just haven't replaced them yet. It probably won't hurt. When mine starts it idles at about 900, and if it starts acting weird, it'll drop a small bit, maybe down to about 500, and go back up a few times, it rarely stalls, it revs itself to like 1500 once, and settles back to 900, and it's good to go. It acctually happens more on warm starts for me, I don't know why. I also think it could be a problem with the MAP sensor, but it seems more like a fuel thing to me.
Good luck, I know how much of a pain in the ass this could be sometimes.

[beretta]

i thought it was a fuel problem so i messed around with the pressure regulator and still nothing. i have replaced the fuel filter when i bought the car this summer, the pump sounds fine, i have no loss of power, just erratic idling on first start up of the day.

when its doing it the scanner counts numerous miss fires but soon as it levels out the counts clear.

Its always done this from day one, but in the summer it wouldnt stall, it would level itself out within the first 10 seconds of running. but now its colder out its being a pain in the butt.

Im wondering if its a ecm issue, the ecm in it is from a corsica to begin with. so im assuming it had a ecm issue before and that was the only replacement they could get. when i get a chance im going to grab one from a 95 z26 i found at the junk yard. but i also think the corsica one gives me a little more performance on shift points, the corsica has 14 inch tires, the beretta has 16 inch, my spedo is out almost 10 KM and its the same any speed i go, im guessing its from the reading of the ecm. it also red lines every gear before it changes if im heavy on the throttle. if im on the highway doing 100 and kick it down it drops to 2nd gear and screams. i dont know if thats a normal thing for a beretta, but i think it has something to do with the ecm as well thinking its going a different speed and messes with the shift points.

Its easy enough to swap the ecm and i want to get a few more parts off that z anyways. i got the front bumper/marker lights/rear upper filler/ dew strips/ power steering pump/ coolant line from t-stat housing/ few other items for 75 bucks. cant beat that.

[SuzukiGhostRider]

GM did make replacement E-PROM's to fix the "cold start , hesitation stumble" upon initial start up for these cars. It's pretty well documented as a TSB actually. It sounds like that's your issue. Your chip has the cold start stumble problem.

[beretta]

is obdII there is not a removable e-prom is there ? my 88 has a removable one.

Going to snag up the ecm from the junk yard when i can get there.

[SuzukiGhostRider]

Nope you're right , missed the year in your post. My bad.

[3X00-Modified]

You cant put a 95 Z computer in a 96, it has to be a 96 computer to work.

A few other things to try is disconnecting your cam position sensor and your crank sensor that's behind the pulley. those two if reading wrong can cause idle issues but will not throw a code. The car will run fine with them unplugged and probably let you know which is causing the issue.

[beretta]

Well i found out the hard way about the ECM lmao. i pulled it today along with the side skirts and brackets and tail lights and few more small things.

Now i have a obd1.5 ecm that i cant use for nothing.

I have a few ecms kicking around from a venture van with a 3400, can i use one of those ?

And.... what ecm from 1997 do i need to get to be able to program it ? does it have to be from a monte carlo ? i found a 97 malibu at the junk yard

[3X00-Modified]

For a 97 ecm if your using DHP it can be any 97 and then you can flash it with either the Venture bin, or a Monte Carlo bin, the Venture one is a 3400 to start though, Monte was 3100.

For HPTuners you have to look at what platform/year is supported and get that EXACT ecm so it will properly register, (still 97 is the only plug and play option for our car) from what I've been told you can't take any 97 ECU and overwrite it with a supported file you own rights to... You need to get/have the proper ECU and license the programming unit to program THAT ECU specifically... I can program any one that DHP supports and as many as I want, I have 2 97's currently and a 96 spare for my car.

[beretta]

So what about a 97 malibu.. im pretty sure it was a malibu anyways and a 3100 in it. its the only 97 i seen there, ill snag the ecm sometime soon.

[3X00-Modified]

This is what HP tuners supports.

GM V6 Cars
Years Avail. Model Type Single Vehicle
Year/Model

97-02 Firebird/Camaro 3.8
00-05 Chevrolet Impala 3.4, 3.8
06-11 Chevrolet Impala 3.5, 3.9
97-01 Chevrolet Lumina 3.1, 3.4, 3.8
97-03 Chevrolet Malibu 3.1, 3.4
06-10 Chevrolet Malibu 3.5, 3.6, 3.9 (3.5 in 07+ only)
97-05 Chevrolet Monte Carlo 3.1, 3.4, 3.8
06-07 Chevrolet Monte Carlo 3.5, 3.9
97-05 Pontiac Bonneville 3.8
97-05 Pontiac Grand Am 3.1, 3.4
06-09 Pontiac G6 3.5, 3.6, 3.9 (3.5 in 07+ only)
97-05 Pontiac Grand Prix 3.1, 3.8
98-05 Buick Century 3.1
97-05 Buick Lesabre 3.8
97-05 Buick Park Avenue 3.8
97-04 Buick Regal 3.8
97-99 Buick Riviera 3.8
09-11 Buick Lucerne 3.9
04 Buick Rendezvous 3.4
99-04 Oldsmobile Alero 3.4
07-09 Saturn Aura 3.5, 3.6

DHP I don't remember if it has a 97 Malibu bin or not but as noted if you have DHP you can flash it with a Venture file and go from there, as long as the last three digits of the service code is 058, that is the only ECU that is plug and play with either the Monte or Venture file. I'm not sure what ECU is in the Malibu, it could be a 98+ style, they mixed and matched.

[beretta]

the last three digits of the service code is 058..

i got one i got one, now what to do with it LOL....

[beretta]

been a while since i have updated this...

so i changed my crank sensor today with one from a 94 i junked the 94 ran fine started right up and idled perfect so the crank sensor must be ok.

I still have the cold start issue, when i crank it over it fires up idles down instantly and stalls out, if i re start it will do the same thing over and over. if i hold my foot on the gas for 10 seconds then its fine.

I have also changed the idle control valve with the one off the 94 because i know it ran fine.

I have never done plugs or wires on the 96, it had always been serviced regularly from the previous owner so the plugs and wires couldnt have been very old to start with but i have put 80,000 KM on it since i bought it April/2011

The 3100 throttle plate has a small pin hole near the center of it.. the 3400 throttle plate i dont think does.. i wonder if that little hole makes that much of a difference for idle.

I guess it wouldnt hurt to do a tune up considering the amount of millage ive done in the past year.

[spacecadetz26]

if you have access to scanner, see if any cylinders are missfiring when you start it up. 96 you should be able to see individual cylinder, you could have a bad plug or injector that needs to be tapped on.

[beretta]

ya i do get miss fires on start up randomly 4,5,6 sometimes other cylinders. but once its running for a few seconds the counts go away..

You thinking its my injectors ?

Would cleaning them help? my mechanic said it was prob my injectors before but people here were saying it could be my cam and crank sensor, i wanted to get the crank sensor changed and see what happend first. my mechanic has a injector cleaning that connects to the fuel line and air compressor. ive been debating if i should just buy my own ($200) on ebay at the most and then id clean them every year.