87 350 TBI idle problem help?

[brans87]

I have a 87 K5 with 350 TBI. I will start with saying has new dist,wires,carp,rotor,Aftermarket egr valve,egr solenoid,full done up throttle body all mods but salad bowl and maybe few things I am missing. Since I put a new egr valve on when I come to a stop and i have to sit for a few it starts idling low and bucking slightly!!! Truck runs great all other time with great power for old truck she will move it. So what could be causing this problem? Also noticed gas mileage went up crazy with new egr valve (bonus!!!) I do notice if put in neutral when problem occurs it smooths out just fine. Anyone will to help me out here?

 

[chulisohombre]

Check fuel pressure coming into the tbi. Mine was doing rhe same thing at first and slowly got worse to where it wouldn't run unless I feathered the throttle. Mine would run but pump was only putting out 4 lbs of pressure. Tbi needs minimum of 9 to run correct.

 

[brans87]

just little up date ran gas down to about empty and put $50 in 93 octane and now truck seems alot better!!!!! Guessing all that ethanol there using or possible other junk was making truck run crappy. Will try some different things and see what happens.

 

[prolinews]

Check fuel pressure coming into the tbi. Mine was doing rhe same thing at first and slowly got worse to where it wouldn't run unless I feathered the throttle. Mine would run but pump was only putting out 4 lbs of pressure. Tbi needs minimum of 9 to run correct.

+1 mine had 10 psi at idle 8 psi under load. I swapped in a tpi pump adjustable fuel regulator 13 psi and runs better than ever. My old pump was less than a year old and was junk.

 

[dyeager535]

It doesn't need 93, if it runs better on it, it's either because the tank is full and you are getting a bit more pressure (if the hose is split is as common now) or you have another problem that the 93 is masking, like detonation.

As suggested, you need to look at fuel pressure, but I'd also be suspect of that EGR valve, they are not a one-size-fits-all component, but are often sold that way. I'd still go after fuel pressure as the very first test.

 

[brans87]

only put a 1/2 tank in truck actually. Know the MSD cap is getting built up with corrosion fast! Thought mabe drilling 2 small holes in side of the cap one on each side to vent????? Wires,cap,rotor,coil all less then year old and less then 5K on them.
Will try to check fuel pressure this week and report back but had a built throttle body with all mods done installed this year.
EGR replaced month ago napa - for 305 motor as truck was 305 from factory according to emission label on support and previous owner installed GM crate 350. I asked about EGR before and go no real answer on the forum.
Don't see why would loose fuel pressure only at idle in drive only. Rest time truck drives great!

Maybe this info will help out

 

[dyeager535]

So you've got a 305 EGR on a 350? I'd have to look at part numbers, I suspect they aren't the same. But at idle, really shouldn't be EGR in any case. Especially with the problem not occurring immediately after stopping.

If fuel pressure is low, but not too low, you will have idle problems but less noticeable issues, if any, during other engine operating conditions. FWIW, in my truck, 43% less fuel pressure SOMETIMES caused real issues at idle, otherwise it would idle tolerably. The GM TBI spec range for fuel pressure is 9-13, even within spec you could see a 31% variation in fuel pressure!

The VSS is hooked up and working? Many get away without it on the TBI rigs, but if not present/connected, may cause issues. You say the wiring is all hacked up, the VSS hangs off the back of the speedometer, feeds cruise control and ECM. If cruise doesn't work, may indicate VSS isn't working right, but there would be more diagnosis necessary.

 

[brans87]

when I say hacked had fog lights,cheap after market gauges,speaker wires and wires that went to nothing ran all over. So far head light switch has 2 wires don't know what they do, drivers seat belt buckle wires cut (no biggie seats are not staying) and few other (3 wires) i had to figure out.
Truck was $1500 with GM crate motor with 20k on it (proved that already) needed transmission rebuilt (had a friend that owns a trans shop fix) then tune up,front end work I did with upper lower ball joints(splicer) front rotors,pads,calipers,bearings. Inside was gut due to smell it use to have but then you can't expect a new truck for $1500. Just trying to get wiring all right and make it great over all rig. So far had year and not single break down while driving it and put 3k on it. I work alot,family,and truck won't fit in my garage so hinders time to work on it. But love driving it and the smile I have while driving.

 

[brans87]

speedo was hooked up and working fine just off 5 mph due to 33x12.5x15