Rough Idle

[Jersey John]

Ok I looked through the post's here and I may have missed it but,

My 95 has a rough idle (doesn't die) and a miss while at cruising speed. It has all new delco tuneup and filters.

Like I said rough idle and cruising speed but when under throttle or load it runs fine with no miss or studder. Is driving me nuts and I did double check all connections and wires for cont. and all is good. I even pulled all the plugs to check gaps. It had a little miss at idle before the tuneup but now it is worse. Any help would be great.

TIA John

[LiftedAWDAstro]

My 95 did basically the same thing. I think the rough idle is a characteristic of that type of fuel injection system. It idled like it had a slight cam in it. I did a full tune-up including ignition module and coil and it ran no different. Under full throttle it ran awesome though! A possible cause could be a leaky fuel pressure regulator in the intake.

[Jersey John]

I'll have to take it to the garage that did the work to have them check it out. It just had new fuel pump, line's, filter & regulator put on it about 500 mi before I got it. It is still under warrenty and it cost my inlaws $1400 to have it all done.

[Jersey John]

I forgot to add before the Sfari has 200k mi on it

Did some playin around this afternoon. As it sits and idle's it seems like it is loading up and it gets a strong oder of gas like it is on the rich side. When it loads up it misses when you first get on the gas then clears up till your just cruising the it starts missin again. Now if you launch hard and keep on it, it falls on it's face about 1/2 way through the r's and start's pullin hard again when it shifts.
It is not throwing out any code's but is just running like. Now it does have a slight leak at the pass manifold where the y pipe bolts on (broken stud) but I don't think that would make that big of a differance would it?

I am at a loss

[rlsllc]

(EDIT: I just re-read your last post, the falling on it's face isn't normal) Sounds normal for a CPI "W" motor ('92? to '95). They seem to like to idle rough. As Dean said, the rough idle is common to that type of injection. Ask Blazer, he drove himself to the edge of sanity trying to smooth out his '95.

I'm guessing that your spider (injector) and nut kit are OK, since your regulator was just replaced, and it is part of the spider. This does make me wonder, though, since they are usually replaced as an assembly.
Although a leaky poppet can give the same results, leaving a fuel pressure gauge on the line can tip off a leak. It should hold 50+ pounds of fuel pressure for several hours after the engine is shut down. If you have any doubt, pull the upper intake and look for clean spots or puddled fuel. These are evidence of a failed spider or nut kit depending on the location of the puddles. It you power up the pump with the upper removed, you can see the leak. (Just be careful!!)

You may want to pull the EGR valve and clean it, and install a screened gasket. That has helped others, but this problem usually triggers a CEL and a code 32, IIRC.


I have a 13K mile spider and nut kit that I'll sell reasonable if you need one.

[BLAZER]

I had two 95's with the CPI injection, both had misses at idle/off idle. I threw everything at them, never cleared up. Like Dean stated, it maybe the nature of the beast, seems the 95's were the worst for it. If they only replaced the FPR, then could be a clogged poppet on the spider injection system. If it's falling flat thow up through the rpm range either it has a fuel issue or could be electrical. Even though the FP is new, I would have them put a pressure check on it and make sure it's getting between 55-62 psi and let it sit to see if it bleeds off even though that would indicate a FPR leak, but since it's new too, probably not the cause. Another thing to consider is electrical in the ignition coil, it maybe losing juice. I checked mine by removing engine cover, and at night, I fire it up with cover off. as I rev motor I watched coil...it began to turn a light blue color ....it was losing juice. Put a MSD or mallory coil from summit on it and seemed to get soem pep back.
Still, after all I installed, it always had the idle miss, sometimes pretty hard, occassionally while excelerating, it was like turning it off, then back on real quick, drove me nuts, but never could find problem. Also remember the EGR is a real screwed up design in these too. It's a linear design meaning it lays flat witht he intake, makes for very easy clogging if carbon breaks lose. Autozone or Advance auto had a filter gasket in the help section to prevent that. Also, small amounts of builup get ont he little shafts and maybe prevents the EGR from opening/closing properly, remove it, clean the shaft (pindle) with some carb cleaner, then re-install..did mine about evey 6 months.

[Jersey John]

Ok replaced the coil. Runs alittle smoother, but it still has the raw fuel smell and still "loads up" while ideling, I am going to pull the upper intake tonight, is there a gasket I need to get of will rtv work ok to reseal it? I tooh it to the garage where my inlaws had the work done and the guy told me $78/hr to check it out and if it was part of the previouse repairs the parts would be covered but not the time. So I am going to check it myself and see what I can find. I'll let ya know soon. John

[BLAZER]

No RTV used on intake, gasket has a small bed of rubber in the gasket that seals it. Should be able to re-use since work was done on it recently, just be careful pulling intake off. Could be a short in the two wires going into the intake towards the front, check them when you pull intake. Once you get intake off, you can turn ignition to start position and watch for any fuel spraying anywhere. If they only replace FPR and not the spider, very good possibility there is a crack in one of the plastic lines ( called a nut kit where it comes into back of intake) Could have a couple of the Poppets on the end of the plastic lines going into motor leaking. Let us know if ya finds anything.

[Jersey John]

Forgot to post.

The fuel preasure regulator went bad on the van and it turns out the garage my in-laws took it to never changed it but charged them for it anyway. So I had my garage put in a new one and checked out everything else that was supposed to have been done and they found the screen in the tank clogged almost completely shut and the tank had all sort's of grit and grime in the bottom of it. The rear brake's that were brand new were shot because they left a drum on that was cracked and the wheel seal was leaking. Cost me over $1700 to get it all straightened out.

Now hopefully I will be able to get most of the money back from the other garage but when we called them they just laughed and hung up the phone so now the lawyers have to get involved and the adventure begine's.