Fillmore has a cold.

[Burbdood 74]

Hey all! I have an 88 Suburban that seems to have a cold. When you start it up, it hunts for an idle, (hi....low....hi....low....), and when you drive down the road, it bucks and snorts, has no power at all and tries like hell to just die out on ya.

It has a new fuel pump, fuel filter, new injectors, TBI base gasket, EGR and EGR solenoid and MAP sensor, (the MAP and EGR valve and sensor I had as spares that I knew were good).

I took it into a shop to have it looked at and the guy hosed me for a lot of $$ and it's just as bad as before. He told me I had a vacuum leak somewhere but he never found it and I can't find it either. Someone mentioned that my IAC could be at fault but I was under the impression that the IAC only operated the idle and had no effect on driveability. Am I wrong and what am I missing?

Please help before I go insane.

 

[Burbdood 74]

Also, it has new plugs, wires, cap and rotor and new plugs and wires too.

I'm also wondering if the pressure regulator on the TBI is on the fritz. IS that too far fetched?

 

[eagle mark]

Hunting for idle number one cause is... ready... vacuum leak.

Someone mentioned the IAC ay? The IAC will control idle if there is no vacuum leak. The IAC still leaks vacuum all the time. If you watch data stream IAC counts go UP not down off idle.

New parts do not mean they are good. I learned this many times long ago! Even if it was a good part was it installed properly?

Back to vacuum leak. Look at a SBC engines intake. Can you see the bottom? Well then you may not ever find your vacuum leak.

How did you test for vacuum leak? What is your vacuum reading and at what elevation are you? The way I test for vacuum leaks is foolproof, it has found them after guys say they did everything to find a vacuum leak.

If you use short bursts of starting fluid around TBI and intake and anywhere there would be vacuum you will find a leak. NOW BE VERY CAREFUL AND IF YOUR NOT? YOU WILL BLOW UP!!!! Because of the volitility of starting fluid it will never be taught anywhere. If you sray it near your altenator it will flare up. If you find a spark it will flare up. So short bursts, long arm, safety glasses and in a well ventilated area. Motor will rev when it sucks in starting fluid. This method has obvious dangers!!! But is foolproof at finding vacuum leaks. If you don't understand why? Don't do it and we will do something else. I have had 2 flare ups in 30 some years and both were near a distributor that had a arcing cap. Because of short bursts, long arm and well ventilated area nothing was hurt, except my heartrate went up a bit!

 

[Burbdood 74]

I haven't used starting fluid, I use carb cleaner instead though. Using this method, I haven't been able to find any vacuum leaks.


I may have to just buy a fuel pressure guage and a vacuum guage and do some more testing.

 

[ccarley]

Sounds kind of like a vacuum leak, especially if it's hunting for idle & not running good. If it were just hunting for idle I might say IAC, but overall running bad could very well be a vacuum leak.

They are tough to find I know. Do you have any codes from the computer at all?

Good luck,
Clay

 

[eagle mark]

Some more equipted shop have a smoke machine that will also show a vacuum leak and if it's under the intake the smoke comes out in crankcase. This is by far best method but the machine is not something anyone other than a shop would buy.

 

[496truck]

My experience with this, my truck would idle hi-low-hi-low for a while till it warmed up. Would also spit and sputter and bog if you went to drive it before it warmed up. Once it warmed it ran great, no issues. Been like that since I dragged it home in 09 and first got it running. Never really worried about it but really got annoyed with it.

Started with a new fuel pump cause that's why it didn't run along with a new filter. After it ran and through the next year I had replaced the IAC, swapped out the TBI for one with no play in the throttle shaft, cleaned out the TBI before it got swapped on, all new TBI gaskets, went through all the vac lines and replaced anything dry rotted or even remotely like it wasn't doing it's job, new PCV valve, new temp sensor, new t-stat, new O2 sensor, removed the EGR and installed a block off plate, all new cap rotor wires and plugs installed before I got the truck and I double checked they were still good, never found any vacuum leaks around the intake, and after all that the truck always did the same thing. No codes, no light.

The other day I rebuilt the fuel pressure regulator, something I had not tried yet. It seems to have solved the issue. I can not say it's gone 100% just yet cause every morning I've gone to start the truck it's been pretty warm out already. But I'm pretty sure it's good to go. This morning it was back to work for me and the earliest (coolest) start up since replacing it and it seemed to run just fine as I was pulling out of the driveway.

Hope this helps in your quest to solve your idle problems.

 

[Burbdood 74]

My experience with this, my truck would idle hi-low-hi-low for a while till it warmed up. Would also spit and sputter and bog if you went to drive it before it warmed up. Once it warmed it ran great, no issues. Been like that since I dragged it home in 09 and first got it running. Never really worried about it but really got annoyed with it.

Started with a new fuel pump cause that's why it didn't run along with a new filter. After it ran and through the next year I had replaced the IAC, swapped out the TBI for one with no play in the throttle shaft, cleaned out the TBI before it got swapped on, all new TBI gaskets, went through all the vac lines and replaced anything dry rotted or even remotely like it wasn't doing it's job, new PCV valve, new temp sensor, new t-stat, new O2 sensor, removed the EGR and installed a block off plate, all new cap rotor wires and plugs installed before I got the truck and I double checked they were still good, never found any vacuum leaks around the intake, and after all that the truck always did the same thing. No codes, no light.

The other day I rebuilt the fuel pressure regulator, something I had not tried yet. It seems to have solved the issue. I can not say it's gone 100% just yet cause every morning I've gone to start the truck it's been pretty warm out already. But I'm pretty sure it's good to go. This morning it was back to work for me and the earliest (coolest) start up since replacing it and it seemed to run just fine as I was pulling out of the driveway.

Hope this helps in your quest to solve your idle problems.

This sounds exactly like the issue I'm having, except for the fact that it runs bad even after it's warm. I didn't notice any problems until after I replaced both injectors because the passenger side injector was just dripping fuel. After I had them replaced, that's when this problem reared it's ugly head. So now my gut tells me the problem lies in the TBI unit......hmmm.

So, it looks as if I'm going to go ahead and rebuild my TBI unit and the pressure regulator and see if it fixes the problem.