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Engine sounds deeper than normal & not staying on after TBI Rebuild

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Engine sounds deeper than normal & not staying on after TBI Rebuild

Old 02-17-2019, 12:36 AM
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Car: 89 Camaro RS
Engine: Chevy 305
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Engine sounds deeper than normal & not staying on after TBI Rebuild

1989 Camaro RS, 305 TBI, T5 Manual Transmission

I've been having a high-idle problem for the past couple of months, and I've been going through and troubleshooting/replacing things. After fixing a few vacuum leaks and giving it to a mechanic that couldn't figure the problem out, I decided to buy a TBI rebuild kit (all the gaskets, fuel screens, O-rings etc). I disassembled and cleaned everything down with choke/carb cleaner, q-tips and some steel & brass wire brushes, obviously being careful with the injectors and only using Q-tips. After everything was back to it's shiny aluminum color and the old gaskets had been scraped out, I put everything back together, replacing a couple vacuum lines and the PCV hose, and put in a new IAC valve.

I ensured everything was plugged in and installed right, and reset the IAC. I ran the car without the IAC plugged in, then with it plugged in, and while I still had the high idle issue, everything ran like normal. I drove it to the gas station, filled up, and drove out in town to pick up a new master-cylinder gasket I ordered from O Reillys. After installing that, I chatted with the workers and walked back outside and tried to start up, but it just kept turning over without catching. I tried pumping the gas, and it almost caught a few times, so I floored it and the engine came on, but sounded a lot deeper than usual, almost like a truck motor (which... it's a 305, but regardless, deeper than usual) and if I let off the throttle, it would begin to sputter and die, struggling to stay on, and then shut off. I got out, took off the snorkel and air filter pan, exposing the TBI unit, which was absolutely drenched in fuel. I tried starting it with the TBI exposed to open air, but got the same result. I disconnected the IAC, thinking it could have been the new IAC, and the car still struggled to start but then "idled" at high RPM, about 2500-3000 without me holding down the pedal. I was able to shift into first and move forwards a bit, to see if maybe something was stuck inside, but it didn't change anything. When I tried to turn the ignition off, it dropped down to a couple hundred RPM, sputtering and choking, but refusing to die. Eventually it made an ugly spraying/hissing noise (might have been the injectors) and then died.

I genuinely have no idea what's going on. This is my first car I've ever worked on, and it's taught me a lot, but I'm still naive as hell when it comes to engine stuff.

The high idle issue I mentioned: When it's cold or raining, the car idles at 1500-2000 rpms and refuses to go down. When I press the gas and come off, it'll stay stuck at 3000, 3500, up to 4000 rpms, and if I quickly tap the gas it usually comes back off and down to 2000. This happens both in and out of gear; If I come off the gas, I'll keep accelerating as if I was holding the pedal down (the pedal is not sticking). When it's sunny and warm out, usually it runs fine at a healthy idle and doesn't stick, but sometimes it still does (Coolant temp sensor? TPS?)

I'm probably going to take it to a mechanic in the morning but if anybody has any ideas on what it might be, that'd be super helpful. I really hope it's something simple and I dont have to replace my injectors. I'm so confused on why it ran flawlessly until it got to OReillys. Thanks in advance.
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Old 02-17-2019, 06:07 PM
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Re: Engine sounds deeper than normal & not staying on after TBI Rebuild

Connect a scan tool, look at the data stream.
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Old 02-17-2019, 06:10 PM
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Re: Engine sounds deeper than normal & not staying on after TBI Rebuild

Originally Posted by Schurkey View Post
Connect a scan tool, look at the data stream.
Thanks for the reply,
I wasnt aware I could connect a scan tool, every parts store Ive gone to has told me my car is too old. What kind of tool and where wouod it plug in?
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Old 02-17-2019, 06:31 PM
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Re: Engine sounds deeper than normal & not staying on after TBI Rebuild

A REAL scan tool--not consumer-grade junk--can connect to certain GM vehicles as old as 1980 1/2. 1981 was the first model-year of widespread on-board computer usage, and scan tools will connect to them.

It's like every other GM. The scan tool connects to the ALDL connector under the dash. The scan tool must be OBD-1 compatible. OBD-2 began in '96, which was a major re-design of the computer/scan tool interface. This is why the dirtbag parts stores can't help you--their junk tools apparently won't work on OBD-1.

Any professional-grade scan tool should be able to communicate with your vehicle. I use a Snap-On MTG-2500 with software suitable from 1981--2006. The MT2500 is more common and nearly as functional. Both are long obsolete--Snap-On quit supporting them in 2009, and quit selling them before that. There may be some consumer-grade tools that will also talk to OBD-1 vehicles, but I've never used one. And there are downloadable programs that will allow a PC to talk to OBD-1 if you also purchase the adapter cable.

Point being, there's no reason to think you should be working on a computer-controlled vehicle without a suitable scan tool. It's possible to do without the scan tool, in the same way that it's possible to walk from New York to California (I'd rather drive, or take a jet aircraft.) The scan tool saves time and effort, can make difficult diagnostic jobs easy.
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Old 02-17-2019, 06:39 PM
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Re: Engine sounds deeper than normal & not staying on after TBI Rebuild

Thanks a lot, I'll look into this and find a proper scan tool or someone that has one.

I took apart the throttle body in the parking lot, and upon inspecting the injectors, found that the upper O-rings had blown out into ribbons. (I didn't know the rings had to be lubricated, the video I was following had every step except that one. Lessons learned lmao) I had to buy a whole new TBI repair kit for those o-rings, but I got new ones and lubricated them with some motor oil before pressing them in, and the car is back to "normal" now. It still idles high at 2000rpm but I've ordered a new TPS and hopefully that fixes it. any other ideas to why the throttle could be sticking?

Sorry for the long *** post with such a stupid, easy fix, but thanks for the replys.
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Old 02-17-2019, 07:23 PM
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Re: Engine sounds deeper than normal & not staying on after TBI Rebuild

An ancient post I made on another forum. This shows the capabilities of a decent (but very old) scan tool on a 1988 TBI K1500 pickup.

http://www.automotiveforums.com/vbul...2&postcount=15
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Old 02-17-2019, 07:30 PM
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Re: Engine sounds deeper than normal & not staying on after TBI Rebuild

Originally Posted by Fenrir View Post
I took apart the throttle body in the parking lot, and upon inspecting the injectors, found that the upper O-rings had blown out into ribbons. (I didn't know the rings had to be lubricated, the video I was following had every step except that one. Lessons learned lmao) I had to buy a whole new TBI repair kit for those o-rings, but I got new ones and lubricated them with some motor oil before pressing them in, and the car is back to "normal" now.
"Self-Inflicted" automotive problems are the worst. Glad you've figured that part out already.


Originally Posted by Fenrir View Post
t still idles high at 2000rpm but I've ordered a new TPS and hopefully that fixes it. any other ideas to why the throttle could be sticking?
Is there something wrong with the TPS that's on the car now?

Throttle cable binding? Cruise cable binding? (No transmission TV cable to bind, since you've got a manual)

DOES THE IAC WORK PROPERLY?

When you connect the scan tool, you'd be looking especially for open/closed loop operation, actual idle RPM, commanded idle rpm, TPS voltage, coolant temperature, manifold vacuum (MAP sensor). Of course, don't ignore any of the other sensors and such, but the ones I listed would be the ones I looked at first.
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Old 02-17-2019, 07:50 PM
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Re: Engine sounds deeper than normal & not staying on after TBI Rebuild

The throttle cable/assy isn't binding or sticking, but it's still idling high. I'd say it's the idle air screw, but the throttle comes to rest on the screw fine and sometimes the engine evens out and idles at proper rpms, so it seems like a computer/sensor issue. I just replaced the IAC because I figured it was that, but I still have the same issue. I dont know if theres anything wrong with the TPS now, but it's old and Im going to plug in a new one to see if it changes, if it doesn't I'll just return the new one. I need to work on finding one of these scanners though.
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Old 02-17-2019, 08:07 PM
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Re: Engine sounds deeper than normal & not staying on after TBI Rebuild

Sounds like a vacuum leak or stuck iac as mentioned above. You can test iac movement by doing the minimum idle speed adjustment. Written for tpi but the minimum setting sequence is the same for tbi.

https://www.thirdgen.org/tpimod2/
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Old 02-17-2019, 11:13 PM
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Re: Engine sounds deeper than normal & not staying on after TBI Rebuild

Originally Posted by Fenrir View Post
I dont know if theres anything wrong with the TPS now, but it's old and Im going to plug in a new one to see if it changes, if it doesn't I'll just return the new one.
Good luck returning a TPS that's been open and installed. Won't happen around here.

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