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Rough idle - running out of ideas - 2002 Astro

7K views 22 replies 6 participants last post by  norohs 
#1 ·
2002 Astro 2WD, late model VIN "X" (no EGR, essentially a 2003 engine) original owner, 196+K. Long term history (major work) is a fuel spider under warranty at 43K, a GM remaned long-block done at the Chevy dealer for a blown head gasket (water in the oil) at 89K. A "hint" of a rough idle was noted as soon as I got it back from the dealer, but it was never addressed - I could live with it and did for another 107K.

New engine long-block 2 weeks ago (oil starvation - oil filter fell off). It's been rough idling since putting in the new engine, but it's been getting worse and worse with each day that passes. Now it's started stalling at or near idle. Runs normal at all other speeds - no hesitation, no misses or surging. It idles well when cold on open-loop. Once it goes to closed-loop in a mile or two it has a hard time idling. I haven't tact'ed it yet, but it's not making or keeping 500-600 RPM's. It's gotten so bad now that it dies getting in and out of the drive - I have to power brake it to keep it running. Just after getting it on the road with this new engine (80 miles or so) I got a 440 code (EVAP). I replaced the fuel cap and it cleared after about 70 miles. Today (800 miles total since new engine block) it set errors for all 3 O2 sensors "too lean".

I've replaced (related to this problem):

plug wires
plugs
distributor cap
rotor
idle air servo
injector spider
air filter
all 3 O2 sensors
thermostat

The TPS was checked both for sending voltage (dynamic) and for resistance (static). It's smooth on the readings and consistent. The mass air flow sensor was spray cleaned with mass air flow spray cleaner. The PVC valve was cleaned and confirmed. Checked the upper intake housing for cracks. Only found cracked seal on MAP sensor but it wasn't leaking- repaired that. New gaskets all around on the intake. Lower intake was RTV'ed across the front and rear deck of block when it was installed. Throttle body cleaned spotless off the intake by hand. Made sure no one ever jacked with the idle rest or idle set screw. Inspected and approved o-ring on the base of the EVAP purge valve. All Chilton torque specs and order were followed. Brake boost manifold tap plug was checked. It is reaching temperature fast and normal.

The highway gas mileage is a bit off at 18.5MPG @62MPH.(indicated on the trip computer). In the past, on this known 20 mile round-trip route with no wind it's been getting 20.5 consistently (again, per the trip computer). I know it could be the new engine needing more break-in time/miles.

Today I pulled the manifold vacuum line to the A/C controls and checked the vacuum - it's 18". Something odd though... I pulled the vacuum line off the gauge and the RPM's climbed about 100 RPM and somewhat smoothed out. That sounded like a rich mixture to me, and with the O2 error "too lean" on all sensors, I thought the sensors were bad (never replaced in 196K). I did run 2 cans of injector cleaner through it before changing the spider. I though maybe the cleaner had damaged the O2 sensors.

The O2 sensors and the idle air controller were replaced today. No change in the idle.

I also pulled the PVC while it was running - no change. Stopped up the end of the PVC and the idle got worse. I found a 3-3/4" o-ring seal that makes sure the throttle body hat is sealed well. To the best of my knowledge, no factory parts are missing or have been modified. No "extra" bolts, nuts or parts left over after replacing the engine. Battery has been disconnected every time it's worked on and allowed to run ("learn") for 10 miles before making any assessment.

On my own, all I can guess at next is a fuel pressure reading and a compression check, neither seems logical at this point. Maybe a re-check of the distributor gear position too. What else should I add to my list or re-check?
 
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#2 ·
Have you cleaned the MAF sensor yet? Even if it looks clean you should clean it just to take that out of the equation. A bad MAF will cause the problems you describe.
 
#3 ·
redfury said:
Have you cleaned the MAF sensor yet? Even if it looks clean you should clean it just to take that out of the equation. A bad MAF will cause the problems you describe.
"The mass air flow sensor was spray cleaned with mass air flow spray cleaner. "

Yes, I cleaned it. It was cleaned off the vehicle and allowed to dry. No damage was seen at the three thermistors nor were they touched.

It was noted that the system seemed to run just a tad rougher and richer after doing so. I expected some change as the intake system had a light oil film on everything due to a long standing oil leak at the radiator (that was fixed a few years back). That oil seems to go everywhere after some time. I'll never put off an oil leak repair again.
 
#4 ·
Some more observations...

On a cold start, the idle and running is without flaw. Once the temperature gets one tick above 100 degrees, things start about a one minute-long "slide" into a low and rough idle. Any touch of the accelerator seems to upset the idle and start an oscillation in the idle RPM's, with the low RPM swing on the verge of stalling. This morning it did die (stall) after a light touch and release of the accelerator. The oscillations have me remembering my engineer school days on the topic of PID control loops and how they become unstable.

Something was noted yesterday...

The idle and stalling issues only happens at a dead stop, so I tried something:

At about 20MPH I put the gear into neutral and coasted to a stop. The idle was good and (for the most part) smooth enough until it slowed to about 1-2 MPH. Then and only then the RPM's fell below normal idle, rough and surging. I did this to see if something was "loading up" the engine at a stop. By being in neutral and just coasting to a stop, nothing was changing so far as any inputs I was making. Seems that the vehicle speed being at a stop changes the way the idle is managed. The vehicle speed sensor is in the loop too.

That sound I hear is my van in the garage begging for more of my time and money...
 
#5 ·
Since it been doing it for 2 engines now. We can surmise it isn't the engine.

Also since you have replaced everything trying to track the issue down at a huge cost in true computers are easier and better style. Just like any shop would do. We can also surmise those parts are good.

Only things left are the wires maybe one got damaged in a swap somewhere, or the computer itself may have a issue on its board.

Are you getting any codes?

Also are there any intake, or air induction parts being consistently re-used.
Air leaks, cracks, Bad seals?
 
#8 ·
norohs said:
Just did a fuel pressure check:

60PSI pre-run when the pump is running
58PSI pre-run after pump stops running
56PSI after and while engine is running

I don't know if these are OK or not.
Those are good.

Go with mahers suggestions.

Sent from AutoGuide.com App
 
#9 ·
chevymaher said:
Since it been doing it for 2 engines now. We can surmise it isn't the engine.

Also since you cave replaced everything trying to track the issue down at a huge cost in true computers are easier and better style. Just like any shop would do. We can also surmise those parts are good.

Only things left are the wires maybe one got damaged in a swap somewhere, or the computer itself may have a issue on its board.

Are you getting any codes?

Also are there any intake, or air induction parts being consistently re-used.
Air leaks, cracks, Bad seals?
I'm (now) willing to spend the $$ for a computer. Can I get a recommendation?

Before I pull the intake manifold back off to re-replace the gaskets, I think I'm going to pull the computer wire harness plugs and degrease/clean them because of the oil grime (oil leak mentioned before). They certainly could use it either way.

More and more though, it looks like I'll be pulling the intake back off on the assumption the something didn't get down tight. The more I think about it, the "slow-slide" into the rough idle sure sounds like a gasket moving and since it happens in 2-3 minutes after starting cold (36 degrees this morning), I'm not convinced that the system is going closed-loop that soon. I guess I wouldn't be the first to have to redo an intake manifold on a new engine.
 
#10 ·
chevymaher said:
Are you getting any codes?
No SES codes ever set before this engine swap except for the ABS and that was fixed with the help of this good site.

Since this engine swap:

P0440 EVAP (replaced gas cap with new - solved)

O2 bank1, bank2 and downstream all showed "Too Lean" (didn't note the code #'s)

P0300 Random Misfire (this one set yesterday for the first time - about 800 miles into this new engine)

After thought....

It's getting worse, it wasn't "that bad" when I first started running this "new" engine, the MPG has been dropping off since (not when) the "new engine" was put back on the road, at this rate of deterioration it won't start or idle in just a matter of a few more days.... Yep, I think I'm going to be pulling the top of the engine back off. *sigh*
 
#12 ·
I like the suggestions to inspect the intake manifold for leaks.. it is a plastic part and could have a crack which is causing the "lean" conditions.

The only line of thinking which we haven't entertained is the transmission loading.. but this is probably not the issue.

Herminator
 
#13 ·
One question for those who know...

Should I use a "film" of RTV on the sealing surfaces of the intake manifold gaskets?

I put the intake gaskets themselves on "dry" (they have rubber seals). I did RTV the front and rear block decks and lapped the RTV up onto the gaskets by about 3/4". I did follow the 3-stage torque instructions in the Chilton's manual.
 
#15 ·
Herman Wiegman said:
The only line of thinking which we haven't entertained is the transmission loading.. but this is probably not the issue.
Herminator
I was thinking transmission too, so this is what I did:

"The idle and stalling issues only happens at a dead stop, so I tried something:

At about 20MPH I put the gear into neutral and coasted to a stop. The idle was good and (for the most part) smooth enough until it slowed to about 1-2 MPH. Then and only then the RPM's fell below normal idle, rough and surging. I did this to see if something was "loading up" the engine at a stop. By being in neutral and just coasting to a stop, nothing was changing so far as any inputs I was making. Seems that the vehicle speed being at a stop changes the way the idle is managed. The vehicle speed sensor is in the loop too."

I think this would eliminate the trans, but I don't know for sure.
 
#16 ·
My brother-in-law made a suggestion today...

Before I pull the intake manifold back off, I might try adding a few foot pounds of torque to the manifold bolts and see if there is a change.

It calls for 132 in/lb (11 foot pounds). I'm going to take them to 15 foot pounds (180 in/lb) and see what happens. I know I can't leave the torque that high, but at least I can note if there is a change. Leaving it there for a full heat/cool cycle might warp the manifold.

I'll report back.
 
#17 ·
OK... Making some progress.

I started off by setting a DIFFERENT torque wrench to 132 in/lb. All the screws took 1/4 more turns to reach torque. I thought it was running a fair-bit better. So, I decided to take them to 150 in/lb. Much better. No more stalling, it's holding idle and a good bit smoother. I took her for a ride and good news/bad news. The engine is definitely running smoother and it's not sounding so much like a bucket of loose bolts. The idle (though a bit rough) is holding RPM's, not surging or stalling. That's the good news. The bad news is that I still have one cylinder "laying down". It's not a dead miss, but she's not carrying her fair share of the load.

So, I will take the intake back off, use FACTORY gaskets and a bit of sealer.

As far as I'm concerned with this thread, I'm calling it solved via leaking intake gasket(s). I'll check back in soon and let you all know how the new gaskets worked out.

Thanks for everyone who took the time to read and respond. Merry Christmas!
 
#18 ·
New user here and first time Astro owner. Recently purchased a $500 Astro van that had been in storage for three years. So far, less than a month later I have installed a remanufactured auto trans, rebuilt the front end completely, new brakes/hardware all the way around, new tires, new A/C front & rear, new shocks, full tune up, new exhaust from the cat back, and a good cleaning. One issue persists, a rough idle when it is warmed up and I stop at a traffic light. The Service Engine Soon light is not on and after a $100 shop charge no stored codes were found and the fuel pressure checks out at idle and after a leak down test and there is no smell of gas at the exhaust when it is running rough. Any ideas before I start replacing parts?
 
#20 ·
I went to a tune shop today to see if the fuel injector skews were off in the ECU. He disagreed about injector problems. He said the shimmy at idle could be this and that. As i eliminated what he offered one by one explaining I had addressed all the ideas offered, he asked if i indexed the flex plate. I said sure (and i did) and then it hit me... I indexed it to the way I found it. Problem is, is that the previous engine (that also had this shimmy) was engine number two. It was on the first day of driving engine number two that when this issue was first noticed. So... if the shop that put in engine number two made the index error, I just perpetuated their mistake (assuming there was a mistake made).

Question is, if i pull the trans and check this, how do i reindex a flex plate... or even identify its not indexed? The only thing i can find is "dont forget to mark it to get the index back correct". Assuming its off, what do i need to do to fix this?
 
#21 ·
In thanks to all of you who contribute and share your knowledge on this site, I thought I would update the rough idle issue I have been trying to conquer in the 5 weeks of owning my 95 Astro van, the issue seems to have been resolved. After replacing plugs, wires, cap, rotor, coil,fuel pump, fuel filter,verifying good fuel pressures running and after sitting, and fixing 4 vacuum leaks the rough idle persisted. It was most noticeable after the van was warmed up and I sat idling at a light. I had cleaned the AIC motor and EGR valve, still no improvement. So, I took the plunge and dumped the cash on a new fuel spider assembly with regulator and poppets as well as new fuel lines. When I had the upper plenum off I noticed that the passage from the EGR valve area that went from the lower forward section of the plenum to the upper was completely clogged with carbon save for a pin hole. I cleaned this out and put it all back together. It ran great for 1 or 2 minutes then ran rougher than ever and got worse from there until I had to ride the gas and brake at the same time. I was done throwing parts and cash at it and took it to a shop that still had equipment that could connect to the GEN1 computer port. They found the EGR valve was dead. It runs like it should now. Had I to do it over I would probably have started where I finished instead.
 
#22 ·
Yeah, gotta be careful of those EGR valves. The problem is that you can't tell from the outside all of the time whether the passage is clogged or not unless you can get a flexible wire to probe through the passageway cleanly. Too bad you plunked down the cash for the spider assembly, but I guess you can scratch that off your short list of things to worry about failing in the near future. At this point, replacing the fuel pump and filter on the van would make the most sense, particularly since the pump on the 95 is still cheap.
 
#23 ·
To update this OP, the problem seems to be coming down to a lean/weak burn in 2 cylinders - #2 and #3. I got the extended PIDs for the Torque App and I am now able to see intermittent misfires when the idle is at its worse.

A "friend-of-a-friend" is going to look at it on his HP Tuners program. Will report what he finds.
 
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