Is it possible that the tb/manifold were not evenly lined up, heat causes expansion, opens up slight leak, but spraying does not affect the rpm enough for me to notice since I’m not looking at the tach when I’m under the hood spraying (I was listening)? Maybe the carbon in the idle air control port of the throttle body is sticking? It was pretty dirty in that shaft
The idle air control motor is malfunctioning, there may be a broken wire or loose connection near the IAC motor. While the engine is running, gently move the wiring harness going to the IAC motor to see is this has an affect on the idle speed.
Unfortunately I’ve tried that but I’m going to mess around with the iac some more in case there’s something going on there even with the new one
Seems to me there was a calibration procedure when I changed mine, but that was some years ago. Check the manual.
Mine I just reset the ecu, but I’ll look into that
I had not cleaned the iac bore previously so here’s hoping that was the culprit!
The way I proved the high idle rpm was caused by the idle air control gadget on my Corolla, I completely blocked that pathway , so no air could get into the engine on that path, even if the mechanism opened fully. Is your IAC gadget configured so that’s possible to do? Caution is in order if you try this, b/c if you block the pathway, and whatever you use to block with comes loose, it will likely get sucked into the engine. Definitely not something you want to deal with.
I very much doubt the problem is that the throttle body isn’t sealed properly to the intake manifold. The spray test would have demonstrated that was the problem. The pressures involved are pretty low, so would require a pretty large opening to accommodate that amount of air flow rate for 1800 rpm idle.
I’m thinking I’ll get it into high idle condition again, pop off the air intake, cover the IAC port and see if it idles normally. Maybe my new IAC is defective
That’ll prevent the engine from idling because air can’t get into the engine
That’s why it’s called an Idle AIR Control valve.
Tester
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Yeah I kind of thought so, saw it on a video lol. What would be my best course of action of diagnosing if it’s the IAC? This IAC is new but it’s not gm genuine
It seems like if covering the IAC pathway caused the engine to stall immediately, that would point to a problem with the IAC path. If air pathway into engine causing an 1800 idle rpm was elsewhere, covering the IAC path might cause the idle rpm to lower, but not stall the engine. It takes quite a bit of air for 1800 rpm.
Ah yes, that makes sense. So if I block the pathway and stall that might tell me that there is no air getting in from other sources, where as if it continues to run I’m likely taking in air elsewhere
Idle air schemes vary greatly, car to car and over the years. Can’t speak to OP’s car, but on my Corolla, there are several pathways for air to enter engine at idle, even though IIRC the main throttle-body butterfly valve (cable operated by gas pedal) is 100% closed at idle.
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air bleed screw. bypasses butterfly valve, manually operated, used (by me) to set warm idle rpm during tune-up.
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idle air control gadget. bypasses butterfly valve, controlled by thermostat-like action by coolant temperature, 100% closed when coolant warm, but opens as a function of coolant temperature, lower coolant temperature, more open. It is possible to completely block this path without affecting any of the other idle-air paths w/ my Corolla’s configuration.
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VSV. Vacuum switching valve, misnomer b/c not really related to vacuum, air-valve, electric solenoid activated, allows air path directly into intake manifold, essentially bypassing butterfly valve, controlled by ECM, activated to open by ECM (or associated electronics) when headlights or rear window defrosters are turned on, used to compensate for alternator load on engine.
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Power steering pump VSV. Another misnomer, not related to vacuum, air valve into intake manifold, actuated by power steering pump when power steering pressure is high. Used to compensate for add’l load on engine by power steering pump.
Mine is this style, it has been replaced once but I’ve yet to do my test, I’m thinking of blowing vape into brake booster when cold, if nothing seems to be leaking, getting the engine hot and idling high and repeating with engine off, if no leaks are evident I am going to take off the intake and block the bypass chamber that the IAC valve closes and if it stalls I’ll assume the new IAC isn’t working properly. I’ve read one comment on a video where he claims that unplugging the IAC while running(which I’ve done several times since owning the car) can “blow” the “driver” for the IAC in the ECU and he claimed to have had to fix several GM ECUs with this issue, which I don’t know if this is accurate information.
Thanks for posting the photo of your IAC gadget. It appears to be a electrical solenoid actuated rather than ambient or coolant temperature. Not sure by its appearance if it is binary (either open or closed) or can also be fractionally open, I’d guess the latter. Do you know if this IAC is entirely closed when engine is warm? If so, you could warm up the engine, turn it off, remove the IAC and figure out a way to block off the opening where that hemispherical gadget seats, then restart the engine. If the idle rpm is back to normal, you’ll know the IAC is allowing airflow when it shouldn’t.
Caution: As mentioned prior, make sure whatever you use to block off the opening temporarily for the test, that it can’t come loose, b/c if it did it could get sucked into the engine and cause all sorts of problems you don’t want.
Aahhhhh yes I think I get what you’re saying, get it to the high idle, remove the iac, block the passage with something solid that won’t get sucked in, if idle returns to normal, the iac is malfunctioning?
If I find it is, and replace it, and still have the same issue, that MIGHT point to an issue with the ECUs operation of the IAC, correct ?
Yes, if high idle is proved to be caused by IAC, and no obvious problems with the surface where the hemisphere seats, & replacing IAC doesn’t solve high rpm, then it could be the computer that controls the IAC. More likely guess though would be a problem in the wiring from the computer to the IAC.
Note: Make sure ignition is “off” and battery negative is disconnected before removing/installing electronic parts like the IAC.
IIRC the IAC on my late-70’s VW Rabbit sensed the ambient engine compartment air temperature. It had a mechanism very similar to what is found under a standard home thermostat dial, a coil spring that rotates as the temperature changes. That rotation opened a sort of window, allowing more air into the engine when the temperature was colder. No computers or electronics involved. Less high tech, but much easier to verify the operation and repair. In my case, that part never needed repair. Maybe a lesson learned, complexity breeds unreliability?
On the Rabbit, the IAC only affected engine RPM. My truck uses a similar coil spring thermostat, but it controls both the engine rpm and the fuel/air mixture as a function of temperature, all part of the carburetor.
I’ll give this a try, though I’m thinking that fully blocking it would cause it to stall in this case, but if I can think of some sort of safe object to slowly insert into the port until closed and see if the idle slowly goes down that might work. I might try the blocking the port from within the throttle body as well. I’ll have to get her idling high sometime this week and screw around and see what happens!
Check the engine RPM sensor and wiring. A mechanic did not reconnect that on one of my older cars after working on the transmission.