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Dustinw · 08-09-2019, 07:23 PM

I have a 1993 P30 with a 454 in it. I start it and it idles at 1450. I have checked for vacuum leaks cant find any
. Changed the gasket on the throttle body, adjusted the idle screw. So far nothing has changed. Still idling at 1450. Any suggestions??

MinntoMich · 08-09-2019, 08:56 PM

I'm puzzled. I have a 93' with a 454 and its throttle body fuel injection. Maybe I'm misreading your post, didn't think you could adjust them. (If) what kind of carburetor does it have? Does the idle come down after its warm?

twinboat · 08-09-2019, 09:02 PM

The idle is controlled by the Idle Air Control valve.
It lets air around the throttle plates and is electronic controlled.

U Tube how to check it.

D Gardiner · 08-09-2019, 10:02 PM

Had the same issue when I pulled my parents 9/95 454 P30 from storage.

There is a fast idle throttle kicker diaphragm by the left side of the throttle body. The throttle kicker raises cold idle rpm by opening the throttle linkage.

The kicker has one vacuum line going to a vacuum solenoid near the passenger valve cover. The other side of the solenoid has a vacuum line going to the base of the throttle body.

On ours, a mouse had chewed through the rubber grommet at the throttle kicker. This caused a very tiny vacuum leak, that wasn't audible. However, because the diaphragm had no vacuum it defaulted to fast idle.

Soppy · 08-10-2019, 07:49 AM

Check for cracked vacuum lines or a bad intake gasket ,stuck EGR or PCV valve.
Had a similar problem on mine and found a vacuum line off on the vacuum canister for the heater controls.

MinntoMich · 09-12-2019, 01:19 PM

Problem solved... A PM response from myself to the OP regarding his high idle problem...

"Okay. You've rebuilt your throttle body, checked for leaks and replaced all sensors/valves/solenoids that would effect a high idle scenario. Providing your work was correct and the parts are working I'd have to say your problem lays elsewhere... But where... Good question. I would have thought you would have nailed it by now.

This was news to me but after a search of a Chevy fourm I found this (link below). Maybe check it out. In short he did a lot of the same work as you and the advice was to check alternator and battery voltage, recheck idle air control valve (plunger, pigtail), verify that no carb cleaner came into contact with electrical connections, and finally possible ECM failure.

The final conclusion of the thread was that the ECM was on the way out which I gather is kinda rare but does happen.

https://www.chevytalk.org/fusionbb/s...hp?tid/311472/

Let me know what your thinking or if this works for you. Thanks."

According to Dustinw, his problem was twofold. First, the ECM "running low and showing a temp of 90 degrees and kept dumping fuel into throttle body." The temp sensor was not changed. Second, an O2 sensor was bad. I'm glad he licked his problem and posted this for the benefit of others who have an early throttle body FI 454.

If I missed anything maybe the OP can add to this thread.

RickNC · 09-12-2019, 03:18 PM

That $23 ECM temp sensor has long been the source of many engine issues on GM TBI and is always the last thing anyone changes. The TBI system weights it fuel mixture calculation heavily on engine temperature and much less so on the O2 sensor. I keep an extra temp sensor in the spares box. It is quick and easy to change and eliminates one known fault in the TBI system. For vaccum leaks I learned this one in tech school back in 1970's.
Use a propane torch un-lit with gas on and point it at suspected leaks If there is a leak it will suck the propane into the engine and the idle will jump momentarily. Safer and less of a mess than using starter fluid or carb cleaner.

glennj3cub · 09-23-2019, 08:48 PM

Can anyone ID for me where the ECM sensor is located exactly and what it looks like for me. Mine just started idling very fast when first cranked up and does not slow down with a pat on the accelerater peddle. It does slow down to normal after driving for a little while (warms up more than it used to have to do).
Or does the 1987 even have one?
Thanks,

RickNC · 09-24-2019, 07:30 AM

Quote:

Originally Posted by glennj3cub

Can anyone ID for me where the ECM sensor is located exactly and what it looks like for me. Mine just started idling very fast when first cranked up and does not slow down with a pat on the accelerater peddle. It does slow down to normal after driving for a little while (warms up more than it used to have to do).
Or does the 1987 even have one?
Thanks,

If it is fuel injected it has the same sensor. On the mid-90's 454 the sensor was located next to the thermostat .I would first check that the thermostat ($8)isn't stuck open. Don't overlook the possibility of a faulty idle air control valve either.

MinntoMich · 09-24-2019, 10:52 AM

I think 88' was the 1st year for a fuel injected 454. The fact that you mention that you have to "pat" the accelerator peddle to take it off of high idle makes me think you have a carburetor.

glennj3cub · 09-24-2019, 11:12 PM

Quote:

Originally Posted by MinntoMich

I think 88' was the 1st year for a fuel injected 454. The fact that you mention that you have to "pat" the accelerator peddle to take it off of high idle makes me think you have a carburetor.

It does have a 4 BL carb!
I have the breather off today, cleaned the K&L air filters. Vacuumed the acorns off the engine and checked the hoses.