1987 TBI Rough Idle Help!

[TruckCo]

Hey all. 1987 TBI with an older Edelbrock Pro Flo FI kit on it. I took my truck out for the first time this year and noticed that once the truck is warmed up to operating temp, the engine idles low and poorly at stop signs while in drive. It idles fine in P and N but when I come to a stop sign the brake pedal shakes almost like I have some crazy cam in it. I replaced the IAC with no luck. It's interesting how this only happens when it is warm. I don't think it's a fueling issue because it only does it when warm. I have heard that when the EGR's go bad it can cause these symptoms however I am stuck. I have no codes and the service engine light has not illuminated at all. Like I said this only does it when the truck is up to temp. It starts great, idles great, and drives great under acceleration it is only at idle under load when the motor sounds choppy and like its going to die. I do not have a tach as well.



Also does i looked on the pass side back of intake and do not see an egr. Did they move them to the front with the conversion? I posted two pics below. Also there is an open vac port on what looks like a solenoid would this cause an issue? Thanks!

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[TruckCo]

Also could this be caused by a bad ignition?

 

[RanchWelder]

Water Temp Sensor at the water neck?

 

[TruckCo]

scanned today. No codes. Just flashed the “12”. I checked the coolant temp sensor. Should the plug be able to turn at all inside the sensor? It moves about a 1/16 of an inch.


Also my EGR if that's what is in the above pictures is a solid dome. I cant stick my fingers in there to see if it moves freely.

 

[fast 99]

Odd you say idles fine in N and bad in drive? That's usually only a 2-300 RPM change.

Check EGR. Most times a finger can be used to pull up diaphragm. If not, need to use vacuum, either suck on it with an extended hose or use vacuum pump. If ok move on to other possible vacuum leak areas, intake, base gasket, ect. If vacuum gauge is available what is the reading? Low vacuum ECM will "think" it's under load and add fuel.

As previously suggested ignition is another possibility. Don't toss parts at it, shot gunning. Take diagnostic steps and eliminate items one at a time. TBI is a dependable simple system.

 

[gmbellew]

Higher RPM can mask other issues. I'd check plug wires for cracks, especially the wire from coil to cap. I'd check the distributor cap for cracks. I'd also check to be sure your exhaust isn't plugged up. Also check to make sure the ICM connector is in good shape, and check to make sure the black/red wire on the ICM connector is actually grounded. Just a few things that have caused me similar issues on TBI that don't usually throw codes

 

[TruckCo]

Ok, i have no cats with FM 40 mufflers and a single wire 02 sensor that was replaced last year. New plug wires last year.

 

[gmbellew]

Ok, i have no cats with FM 40 mufflers and a single wire 02 sensor that was replaced last year. New plug wires last year.

I've had new AC Delco wires last less than 2 years before they started letting the spark out. Just because it was recently replaced doesn't mean it is still good. With no codes being thrown and nothing odd in the sensor data (I assume), you have to start looking at other things that could cause these issues. Likely it isn't fuel if it is doing well at higher RPM. Ignition components are high on the suspect list. Plugged up exhaust is unlikely with no cats. Is it getting rich at idle?

 

[fast 99]

On the distributor cap front, have seen cheap non Delphi caps crossfire inside the actual material they are made from. Should affect other areas of drivability.

 

[TruckCo]

I'm not sure exactly what running rich is on a FI , it smells like an old truck and there is no excessive smoke. I am trying a new coolant sensor and will report back tomorrow when the weather is nicer to take for a drive.

 

[gmbellew]

I'm not sure exactly what running rich is on a FI , it smells like an old truck and there is no excessive smoke. I am trying a new coolant sensor and will report back tomorrow when the weather is nicer to take for a drive.

I figured your fuel injection system had a computer readout? Rich is O2 values steadily near .8-.9v and the computer would be reducing the short term and long term fuel trims.

 

[TruckCo]

Update. I replaced the coolant temp sensor and it has been running great since.

 

[RaysnCayne]

Wish that worked for me.
I'm running rough and rich and thought I was smart (after some YT and forum searches) and went right to the temp sensor change (bought a GM one to boot). But no change for me.

 

[Ricko1966]

Wish that worked for me.
I'm running rough and rich and thought I was smart (after some YT and forum searches) and went right to the temp sensor change (bought a GM one to boot). But no change for me.

Have you checked for vacuum leaks,misfires,and tested the map sensor?
A little diag tip for people troubleshooting rich on injected cars. A bad plug,plug wire, will result in 14 parts unturned air,but only 1 part unturned fuel making it to the O2 sensor,so the computer sees extremely lean,even though you smell rich. The computer pours in the fuel trying to compensate for the lean condition its seeing. So if you have a noticeable miss check ignition,your rich condition might just be an ignition problem.

 

[gmbellew]

do you have a tach, or can read the signal from a scanner? a jumpy tach could be a bad ICM ground or a plug wire touching computer wires or a bad plug wire or cap letting the spark jump to computer wires.