1987 Chevrolet 350 tbi high idle

[Rusty Nail]

Bingo!
Throw the 160 stat in the trash and install a 195.

The computer can/will make adjustments for UP TO FORTY key starts unless you reset it. Second best thing you can do to cure its' ails is unhook the battery while you switch thermostats. Bet it otherwise fixes itself outside of proper procedures including but not limited to bleeding the coolant system.
No air bubbles found in closed loop.

Let us know and good luck!

 

[Vbb199]

If it's any interest to you, I purchased and setup a scan tool that's Bluetooth compatible, works with obd 1 and 2. The device paired with a 5$ app allows you to view live ECM data from your phone, see codes, and whatever else. Very nice.


In terms of it sitting at 1200+ rpms, is the throttle shaft just stuck maybe? Can you pull the arm back and make the idle go down?

Maybe carbon build up in the tbi?

 

[Vbb199]

Bingo!
Throw the 160 stat in the trash and install a 195.

The computer can/will make adjustments for UP TO FORTY key starts unless you reset it. Second best thing you can do to cure its' ails is unhook the battery while you switch thermostats. Bet it otherwise fixes itself outside of proper procedures including but not limited to bleeding the coolant system.
No air bubbles found in closed loop.

Let us know and good luck!

Engine/Coolant Temps are single hardly the most critical thing on a tbi motor, since the cats dictates a large portion of operation

 

[iamtherealJayy]

The throttle cable returns fully to its position with no drop in idle speed. I reckon I’ll change the thermostat to a 195 today since it is getting cold and it would be nice to have heat through winter. What should I use to clean the iac to make sure it’s clean?

 

[iamtherealJayy]

And if you could recommend a decent affordable way of checking live data through ALDL/OBD1 let me know, I can’t use the aldlDroid stuff because I’ve got an iPhone.

 

[gmbellew]

I doubt the 160 thermostat is causing it to idle that high. but the 195 is the proper temperature to run.

if you can't check the IAC operation with a code reader I'd follow the procedure I linked in post #8 to check the minimum idle speed by taking the IAC out of the equation. you will need to hook up a tachometer temporarily. if the minimum idle speed checks out, you very likely have an IAC that has gone bad.

 

[iamtherealJayy]

Everything I read from that previous link required a code reader? I don’t have a code reader and can’t find one worth purchasing. I’ve done the paperclip and read the flashes before and the truck had no stored codes. I don’t think the thermostat is the problem either it had a 180 in it for the longest time and idled the same way.

 

[gmbellew]

the procedure I linked doesn't require a scan tool if you hook up a tach. you just need a paperclip to ground the ALDL to force the IAC to close.

 

[iamtherealJayy]

I have a tachometer. I installed it forever ago to monitor rpms, I’ll go back and re-read since I misunderstood the first time. I’ve heard so many different things about why it idles high rolling to stop lights and one is because of emissions or something but it doesn’t make sense why in low I can get it down to 800 before it violently shakes and push clutch in and it shoot back up like I just started it.

 

[iamtherealJayy]

Here’s a little more info on the truck, first time I ever asked why it idled high I was told the timing was advanced so I got the timing light on it and it’s 8° btdc and I looked into it and 4-12 is factory so I don’t think the timing is too far off. All the smog stuff is still on the truck, air pump, canister on rad. support, egr, it’s all there. The truck hasn’t had any modifications done other than the block was replaced at one point but it’s factory tbi heads up. Another completely unrelated question is about my oil pressure gauge not working, it’s fully pegged to the right at like a 3 o clock position, I tapped on it once and it moved around a little but when I turned key on it jumped right back to that position.

 

[iamtherealJayy]

I read the second part of that forum again, if the rpm is still too high is there anything to do other than puncturing that plate and adjusting the idle? Or is that the only way. I’m trying to keep it as factory as possible for now.

 

[gmbellew]

factory timing is 0deg BTDC.

there is no other way to adjust base idle.

I would wager that it is more likely the IAC has gone bad than the base idle is off. there is a reason it is covered....it shouldn't really need to be messed with.

another thing to check would be routing of the harness to all the sensors. move the harness around and make sure something isn't getting pinched or getting voltage when it shouldn't be...do this with the engine running so you can hear RPM changes

 

[gmbellew]

I am not sure about the oil gauge. but it sounds like either the wires are crossed at the pressure sensor, a bad pressure sensor, or a wire is grounded that shouldn't be in the sensor wiring.

 

[iamtherealJayy]

I just drove for a bit and connected the paper clip and turned ignition on and service engine light started flashing and I could hear a clicking sound from I assume the iac?

 

[gmbellew]

not sure on the clicking sound...but it could be the IAC trying to close. if it is clicking audibly, maybe it is stuck open or something.

the check engine light flashing is showing any stored codes. it should flash 12 three times (one flash, two flashes for each 12). then flash any stored codes in the same fashion. then flash 12 three times again.