Strange idling issue

[Clockmaker]

Hi everyone I'm a "Newbie" here and have a question to ask.
I am having an idling problem ....
These are the facts as follows...

Model 1993 C/K 1500
100,500 miles on the engine, no oil consumption, changed every 2500 miles or 3 months which ever comes first.
New fuel filter, installed correctly
Cap and rotor 20,000 miles since replaced
same with plug wires
Used seafoam last week
Sprayed the TBI and cleaned the varnish off of the inside of TBI.
Checked for drip from TBI injectors with key on, no drip.
Fuel pressure good
Have not checked for codes yet..
No, " check engine light" on either.
Gas mileage has dropped..
No black smoke coming from the tail pipes, however, the pipes are sooty indicating a rich condition
No popping or back firing on decel or accel.
Depending on the engine temp the idle is sometimes very low 300 or 400 rps.
I do have all of the manuels for this model.
Engine temp is normal and reaches operating temp as normal 195 degrees.

Symptoms : On first cold start in the morning the engine revs up to 1500 rpm then setttles down and idles smooth no misses or shakes, and drives with a good pedal response.

On the next start up 3 or 4 hours later engine idles rough with low rps antenna shaking and interior seats shaking as well????

Pedal response is strange...as your pushing down the engine seems to not want to accelerate then catches up...this is a pain in the a_ _.

I have read the posts on this forum as far back as September on "Idleing" issues and I am still puzzled, can anyone shead some light on what or where I should go next.

I have planned to replace the TBI gasket and clean the EGR this weekend, that may help from what I have read.

If there is anything else that will be helpful (facts) that I have left out please ask...

Thanks, George

[BobM46128]

What engine?

[Clockmaker]

Good grief...I left out the most important part..."350" my bad...!

[joe92k1500]

Cleaning the egr is a good way to start. At the same time check its operation. Make sure it moves when the engine is cold and warms up to normal temp. Also check the plugs and examine them. Make sure the gap is ok and there are no signs of abnormal wear. It is probably a good idea to replace your O2 sensor. They dont always give a check engine light when they are not working right. Oh yeah, take a look at your IAC too. Let us know what happens.

[Clockmaker]

WIll check the EGR & IAC Saturday,

I replaced the plugs at 6/6/2003 at 92,450 miles may replace anyway because the truck is used for work mostly, round trip 15 miles.

I replaced the O2 sensor on 8/15/2003 at 94,280 miles.

Thanks for the info...joe92k1500

[Clockmaker]

UPDATE:

Checked the EGR it works and is somewhat clean so I left it on the truck. The piston moves back and forth and seats with no leakage.

Repalced the IAC with another one, adjusted the plunger as recomended no more that 1 1/8" from the tip to the seat, It was out of adjustment from the box it was set at 1 1/4"from top to seat.

Replaced all of the plugs, they were all ok anyway with no carbon or sooty look. All of them were an off white color, a clean burn.

Did a test ride the initial cold crank was different and did not rev up near as high as it has been doing cold. It may be in my head but I think it runs different and idles better.

Let's see how it runs Saturday.

[rhaack]

my '93 runs terrible when hot, great when cold as well. The only thing I've been able to find on this is a vacuum leak, of course pumping the brakes corrects the idle. My oil pressure gauge also drops with the irregular idle. Every "professional" I've taken it to said it runs fine, I guess I'm in the same boat as you............

[rhaack]

I did buy a Hypertech thermomaster chip with 160 degree thermostat, truck runs a lot better and gets way better gas mileage.

[Clockmaker]

Mine runs best at about 195 to 200, can't complain about the truck to much it has never been in the shop at all. The oil pressure problem is your sending unit that can be fixed, mine does it also just haven't replaced the sending unit. I fixed the problem with mine so far I replaced the IAC, cleaned the EGR & replaced the plugs...so far so good...knock on wood.