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I need your guy's help with rough idle issue

7335 Views 71 Replies 12 Participants Last post by  astro355
Ok, 91 astro AWD... I've changed every sensor except the TPS and the main computer and it still idles rough (rough enough it shakes your brain while your sitting at a light). It will occasionally stall but only going into reverse.

Above idle it still runs great and pulls hard with no oil burn or black smoke.

I also changed the injectors, map sensor, knock sensor, coolant sensors, egr solenoid, cleaned the egr itself (wasn't really dirty).

The van only has 250,000 kms on it so this is really tickin me off.

Put a new wire set, new plugs, new cap & rotor, checked the timing, replaced all the vac lines.

Not sure if it's related but the cruis control doesn't work either but has great vacuum going to it.

I was gonna do a V8 swap but I can't get the mounts for a reasonable price or find a good set of plans.

This is our daily driver and hauls our 4 kids around so if anyone has any ideas please let me know.
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i don't know honestly... he plugged it into the ADL port thingy and ready the codes, then started the van and read more crap, went into a few different menus and changed something or other... I thinkhe did a full scan, or at least he said he did... took about 20 mins total.

That sounds like a scan tool.Do you know what the fuel trims are ? Maybe you could try some seafoam or power foam through your air intake .
OK, if it is showing rich, then it is not a ignition/misfire issue. A missfire would show up as lean.

Fuel pressure is where you want to look next. High fuel pressure in a TBI unit(14psi+) will cause a rich code.
The fuel pressure regulator spring is probably broken, or plugged with gunk. It is located on the TBI unit, between the injectors, and just behind them. If you remove the Torx screws that hold the injectors in place, and remove the top, the regulator is on the underside held in with 4 small screws. Remove them, and see what kind of mess you have.

A new regulator is about $75, and comes with a new cover.
Not sure what it showed but he said fuel pressure is 12psi steady.

I have a spare tbi here so i'll rip it apart first to see whats in there.

Man I hope this fixes it... i'm out of idears.. lol
Vacuum leaks maybe? Cracked lines going to a vacuum source like heater control valve or cruise control ? Faulty MAP? Faulty EGR. or Temp Sensor? Just a thought.
Ok replaced the fuel pressure regulator today with a brand new rebuild kit.... no change :banghead:

Re-Checked the van lines using propane... no leaks :banghead: :banghead:

I am so stumped... last ditch effort is pick-n-pull for a used computer i guess :banana: :canada:
Gordon said:
...The only smoke i ever get is the cold startup blue cloud...
We had an 88 Beauville van (350) that idled really high (& blew blue cloud at start up)for the first year or so we owned it. I tried so many things trying to get that idle down; vac lines, fuel filter, TPS adjustment, etc. Turned out the throttle body gasket had huge gaps in it in spots I couldn't see it until actually removing the throttle body.
I know it's not the exact symptoms you're describing, but... :rock:
I replaced the TBI gaskets when I replaced the TBI itself.

I found a 1990 rwd as a donor... runs great but its written off from being rear ended.

I'm gonna steal its motor for our van and the rear posi unit as ours doesn't have it.

Whole van for $50 and it runs perfect.

I'm gonna swap computers before I yank the motor though just to be sure...

Thanks guys :banger:
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Have you checked the engine to body ground cable. Also take the battery to engine ground cable off and scrub it up make sure there is not oil on it causing a bad ground. From what others have said these vans are also picky about what cap and rotor you use try some AC Delco parts and see if that makes a difference.

I just went thru a huge problem with back fires and replaced darn near every sensor before I finally fixed the problem so I feel your pain and know what your going thru.

Have you replaced the throttle position sensor???
Yup checked and replaced the factory grounds and added a new one to the alternator itself.

First thing I changed was the TPS sensor.
:confused1: I just got a 93 Astro and it idles like crap. Saw some gasket peices like someone has been in the intake manifold and a new EGR was installed . I have replaced plugs wires cap rotor,,,,although now I am thinkin AC Delco on the cap and rotor would be good.Hmmmmmm
I gave up trying to figure out my rough idle so I found a used engine to replace it.

I have a feeling it was something internal.
It may not be your engine but I got to the point of saying why bother putting more money into it.

I think i spent about $500 just replacing sensors... the only thing i didn't replace is the computer itself.

Before I actually pull the engine out i'll swap computers and see if that helps.

I'll upload a video later of my rough idle so you guys can hear what i'm talking about.
So today i took her to a shop. They checked the EGR valve. all was well. They checked the compression. All was well. None of the usual suspects such as TPS or IAC came up bad. no vac leaks fuel pressure right up there. Plugs and wires good....cap and rotor too (no juice leaking out,,,,, all firing. The mech noted high hydrocarbon in numba 1 cylinder,,,,indicating incomplete burn,,,for some reason,,,,perhaps a broken valve spring,,,,but doubtfull. The only question mark is the valve train. His best guess though was the fuel injection,,,,,which is consistent with what is known and expressed here and elsewhere about these particular systems.

So.........................After I take off the valve covers to confirm no broken or loose springs AND verify that this motor was not a replacement that originally had TBI injection (apparently the TBI injected motors had adjustable rockers and a different cam that do not jive with the later csfi or cmfi systems) I will order the Linder Tech reconditioned fueld injection kit with new and improved fuel regulator. Tonight I wil pray.
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Yo Gordon

It may be academic now but one thing on those Throttle body injection units was worn butterfly rod bushings causing rough idle, amongsnt other things. Linder tech lists that as one of there services when rebuilding a TBI. I have a 1/2 truck on which that is the case.
Here's a concept many are overlooking. No codes no issues with the computer as such. Rough idle indicates a typically non contributing cylinder. That includes compression, ignition, injection, etc. Usually, these engines have issues with the spider, or injection assy. First, determine whether it is an issue of one cylinder. If it is, try disconnecting the plug wires, one at a time, until one, when disconnected, has no effect on the engine performance. That cylinder is the issue. Go from there. Ray
Hi Gordon
The idle stumble can be a pain for sure. Have you pulled the EGR vac line and plugged it off to see if it made any difference? You said you cleaned it but didn't mention if you checked the vacuum on it. A short in the spark plug wires can cause a a bad stumble. Also, if you replaced the plugs, you may have cracked one or even have the wrong plugs in their which will do the same thing as you described.

Have a look at the exhaust as mentioned above and smell it, if it smells rich, then it could be something related to fuel. If the exhaust doesn't smell rich, then start pulling spark plug wires at the distributor while the motor is idling and to see if you can narrow the stumble down that way. You need to eliminate each area first (Fuel-Spark-Air). Hope this helps. :)
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I should mention that this van is TBI injection and not CPI so there is no spider assembly or crossover.

Exhaust smells normal.

Motor is pulling 15 inches of vacuum at idle and upwards of 30 when revved.

If I pull cyclinder #5's plug wire off there is no change in the idle so that's the problem cylinder.

However the confusing thing is that the compression is good on all cylinders, the plug wires are new and I tested them for resistance when I put them on, the plugs are also new and where tested and gapped before install.

The only thing that makes sense to me is either a bad computer in general or a blocked passage in the intake manifold reducing the fuel/air into that cylinder.

I have pretty much learned to put up with the rough idle as my parts van deal fell through so i'm stuck with this crappy engine for now.

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Hi Gordon
Well that's good #5 cylinder. Was this problem there before or after the plug and wire changes? It doesn't really matter
what anything says at this point, you could have cracked the porcelain on the plug while installing it or pulled on the wire without realizing you had. This happens more times than you think. Anything relating to #5 check. That's including the #5 terminal inside the distributor cap as well (pull the Cap). If the distributor cap is a bit off, it could strike that post and cause a bad miss. Are these after market or OEM items you installed? Please keep us updated, Thanks.
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