TBI idle issue

[iamtherealJayy]

I’ve had a previous thread and it went all over the place, I’m here now because my problem is back and I never got a fix. 1987 Chevrolet V20 350 TBI Frankenstein engine and sm465 trans. The engine is a tbi from heads up but has an older block. Cold start idle to warm is fine and truck idles around 650/700 according to cheap tach. But if I “blip” the throttle it’ll jump to 1200 then like 1600 and hold there for a split second before slowly dropping down. Shifting gears I can be at 2500 rpm press clutch in and it might drop to 2000, I can pull it out of gear to sit at a stop sign and the truck is sitting at 1600 rpm. I’ve replaced loads of parts, some helped temporarily others had no effect. I’ve heard the idle staying higher while coasting to a stop is common others say otherwise. I don’t need it race engine snappy return to idle but I’d like it to Atleast drop below 2k while shifting? I’m just trying to give this tbi setup one more chance before I try to ls swap it.

 

[gmbellew]

I don't remember all that you tried before. but I'd start by 1) forcing IAC closed by grounding AB on ALDL and turning key on for 30 sec. then unground it and start it up. see if that fixes it. if not 2) disconnect EGR hose between valve and solenoid. plug the solenoid side. see if that fixes it. if not 3) follow the EGR diagnostic in the drivability manual to check the solenoid. if that doesn't fix it, 4) check EGR operation with a mityvac. if that doesn't work 5) find somebody to smoke it for vac leaks, assuming you have already checked the various hoses for the MAP, EGR, PCV, etc. then 6) hopefully you have a aldl reader and ALDLdroid to make sure all the sensors are doing their proper thing.

 

[iamtherealJayy]

IAC was replaced with AC delco and verified working(at the time) egr is new from oreillys (one of two times left stranded by this truck) there’s no obvious vacuum leaks, MAP is new along with ECTS(EngineCoolantTempSensor on the intake) and the TPS, throttle body was removed regasketed and cleaned. I do have RedRiver? I think, ALDL but I could never get it to load onto my laptop I couldn’t figure out how to use the software to match my truck on the recommended program. My issue wouldn’t be so bad if I could just ease into the throttle but it’s like you’re trying to barely press the pedal and it jumps up to 1600-1800 and takes forever to come back down. I like the tbi system for this time of year being 20° F of a morning (my 78 carbed still starts, actually quicker than this one) and I like the fuel mileage(12-13 when it’s running right) I’d originally got the truck and it would hardly run on 87, wouldn’t idle at all so I ended up changing two sensors I believe MAP and ECTS and that resolved that issue but this high idle thing has been an ongoing issue. Along with my hydraulic clutch system. Other than that the truck runs phenomenal. I’m just trying to save on this TBI if I can.

 

[gmbellew]

EGR shouldn't leave you stranded usually. make sure the EGR is the right part, there are a couple different kinds and it matters which type.

did you check the throttle linkage for smooth operation? does it do it if you blip the throttle from under the hood with the throttle cable disconnected from the pedal?

ALDLdroid app is pretty straightforward with a Droid phone or tablet. it has default files you can choose from to get data. plenty others out there on the various tuning sites.

 

[iamtherealJayy]

My egr didn’t necessarily leave me stranded the truck started but idled poorly the egr seized and had a vacuum leak, off idle tan fine but it wouldn’t idle. The throttle blip does still fluctuate from under the hood I haven’t tried with throttle cable disconnected but I can. Using my hand to move the throttle linkage it feels to move fairly well, and with truck off I can pretty easily press the pedal to the floor but when it’s running I feel as if the pedal is stiff and when I get it to “break free” is when it revs to the moon. It makes it hard when in a lower gear trying to move and the truck is at like 800 rpm just creeping and you try to hit the throttle it almost always jerks you back in the seat and chirps the tires. Like earlier my ole lady wanted an ice cream cone so I stroll over to the local McDonalds and get her one but when going through the parking lot I was in low moving at **800 rpms, and I tried to ease into the throttle and the truck started bucking and acting a fool I felt like a damn bull rider in the mcdonalds drive thru.
Edit: I cannot use the droid variant as I do not own any android os devices. I’ve got an iPhone and a windows laptop. I tried using the Aldl to usb cable and one of the programs provided but it required a file to be added of what vehicle it was and I couldn’t ever get it to connect correctly.

 

[gmbellew]

If the TPS is changing voltage evenly across the range from idle to WOT, I'd be looking for something mechanical in the throttle linkage, throttle shaft in the TB, or something like that. it doesn't seem like it is a computer/TBI issue from what you describe of all the main computer control sensors being new. although it would be better if you could verify they are working with the cable or a voltmeter.

 

[iamtherealJayy]

I did probe the wire to the tps and it read in the range recommended but I don’t remember much else from when I tested it. I’ll try tomorrow to see how it acts with the throttle cable removed and using the linkage with my fingers. Possibly WD40 the linkage?

 

[iamtherealJayy]

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Here’s a link for the sound from idle and blips of the throttle.

 

[iamtherealJayy]

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Here’s a video of the throttle body with the air cleaner off. I notice fuel pooling around the rear of the throttle body. Throttle cable removed doesn’t make a difference on return to idle speed, I can close the throttle manually and it will lower the idle but fuel puddles on top of the throttle blades.

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The “yellow” look around the “TBI” is fuel. What would cause fuel to go everywhere other than the intake?

 

[gmbellew]

wonder if the extra fuel is keeping rpm high until the computer can compensate? I'd fix that issue and then re-evaluate.

 

[iamtherealJayy]

What do you suppose is causing the fuel to puddle everywhere? Last time I worked on this issue I replaced the base gasket under the throttle body (lowered idle some fixed vacuum leak) and I cleaned it while it was off.

 

[Bextreme04]

Have you rebuilt the injectors and regulator yet? Extra fuel like that could absolutely be from the wrong fuel pressure or leaky injectors. That would also cause some drivability and idle issues like you have described.

 

[iamtherealJayy]

I haven’t touched the injectors or regulator, where’s the regulator located? I know where the injectors are lol.

 

[gmbellew]

I haven’t touched the injectors or regulator, where’s the regulator located? I know where the injectors are lol.

pull the TBI off and replace the gasket under the fuel pod cover, injector orings, pressure regulator gasket, etc. clean carbon out of the passages, etc. I'd just get the AC Delco rebuild kit and do it all. the kit is about $35 and it ought to take you a couple hours start to finish.

 

[iamtherealJayy]

I’ll look into it thanks.