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I need your guy's help with rough idle issue

7337 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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cleaned the original, didn't change anything at all so i bought a new one... still no change
Warm or cold it runs the same.

No codes.

Sprayed with carb cleaner... no vac leaks.

The only smoke i ever get is the cold startup blue cloud.

Would a torque converter solenoid also make it idle like crap in park or neutral?
No leaks and no stumble.

Compression test shows 140-145psi on all 6 cylinders.

Once you pound that pedal down she takes off like a bat out of hell and pulls strong to 6000rpm without missing a beat.

If someone happens to have a set of AWD V8 mounts to sell or plans top make them let me know... i have a 350 sbc lined up already for $300.. it's a 1994 tbi motor already pulled for me :D
Pumps working but i have not pulled it out of the tank to look at it.

Filter has been replaced.

You'd figure if it was a fuel issue that it would also be starving for fuel in higher rpm's, not just idle.

The spray pattern is a nice clean cone also, no drips.

This one is TBI so no spider assembly in it.

Keep the ideas coming maybe we'll hit on something :confused1:
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ARG... now i have a code 45 today... O2 sensor rich.

Stupid thing is only 3 weeks old... i'm gonna blow this van up soon :cussing:
Changed it when i did the cap and rotor.

As I said I have replaced almost every sensor and part on this POS van.

I'm so tempted to put a brick on the gas pedal and let the v6 blow :devil:
Where would I find this item?
I had a friend throw his Snap-On scanner on it today and everything shows normal :banghead:
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.

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
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:
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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Yup checked and replaced the factory grounds and added a new one to the alternator itself.

First thing I changed was the TPS sensor.
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.
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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The #5 problem was there before i changed the plugs, cap & rotor.

I've checked the plug wires, plugs, cap and rotor since I installed them and there is no change.

I was thinking maybe a valve but the compression is good.
The I figured maybe a bad ring but same thing... good compression.

So I did a leak down test on that cylinder... stayed up for over an hour.

The computer has nothing to do with this I don't think.

The injectors are firing when they should, the timing is dead on, no vac leaks, etc.

I even double checked the firing order just to make sure i didn't make a noob mistake there but it's all good.

If I could have just found a set of AWD V8 mounts I would have had this solved by now :help:
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Oh and all the parts are aftermarket.

Plugs are AC Delco
Wires are Bosch
Cap & rotor are also AC Delco
No vac lines going to the cylinder itself.

I had the valve cover off and checked the lifters with a torque wrench... all is good.

Timing is 100% dead on 0 degrees BTDC (set with the brown/tan wire disconnected as its supposed to be).

Had the plug out yesterday (damn van cut my hand of course on that cylinder) it's clean and the threads are normal and not binding at all.

PCV valve is new and passes the "shake" test.

The thing that confuses me so much is that it has good compression but disconnecting the plug wire makes no difference to the engine at all.

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