454 TBI Idle problem

[carl2015]

I've been a member for a couple of years, don't post much, but have learned a lot just by reading posts.

I have a little problem with my 1992 Winnebago P30 454 TBI.

Once it reaches operating temperature it seems to try to die when idling. This happens about every 3 to 5 minutes. ONLY when hot and ONLY when idling.
It started acting up on our last trip. tried to die at a red light and again when we got to camp ground. When we left 3 days later, went to get gas before trip home, didn't act up, but it was a short drive to gas station so probably wasn't really warmed up yet. Drove it on interstate for 95 miles no problems, stopped to get gas at last station before home, and it tried to die when I pulled up to pump. Drove the final 25 miles home on highway, no problems till we got in driveway.

When I run it in the driveway, it needs about 20 mins before it will start acting up.

I hooked a code reader up to it, no codes.

I went ahead and changed the O2 sensor
no change.

O2 sensore voltage runs from about 200mv to about 700mv.

I do notice that the EGR reading on code reader stays at 0.

I have not found any loose connections, or wires grounded yet (still looking). I don't see any loose vacuum hoses either.

Going to go ahead and go to Harbor Freight and pick up a fuel pressure gauge and hook it up tomorrow and see what it tells me.

[M & J]

Youre on the right track. Google about the IAC after you check the fuel pressure. No check engine light or codes you say. FP iscthe next obvious check.

[DaveVA78Chieftain]

From 1992 Chevy Light Truck Fuel & Emissions Manual (OBD1)

[TerryH]

Youre on the right track. Google about the IAC after you check the fuel pressure. No check engine light or codes you say. FP iscthe next obvious check.

I agree with Mike.
FP possible.
IAC very possible. First and easiest check is all battery connections. Power and definitely ground at both ends. Good to check, clean and tighten regardless of problems.
Suggestion - if you have access to another code reader try it. Always consider the 'Made In China' syndrome.
I like to check what can be with relative ease before the dreaded 'throwing new parts at it to see if they help'.

[carl2015]

Definitely not the fuel pressure, stays rock solid at 13 PSI.


https://youtu.be/zP1ToTjXG1o


I also unplugged the temperature sensor to make sure the code reader would show it, it did.


Here is a video I made before it was fully warmed up


https://youtu.be/LOgq5fu68Sg

[FJR1300]

Stupid question but,...looks like your checking the fuel pressure under to coach? Not under doghouse at the carb? Is there a filter on the frame rail?
Just that symptoms sound quite similar to mine 2 weeks ago..and a filter change was that answer.
Have you taken off the air filter cover to observe injector spray?,..
Don

[carl2015]

Yeah, there is a filter under there. The pressure kit I got has an adapter, you remove the filter and put the adapter inline and hook gauge to it. The filter has been replaced.

[carl2015]

Thanks for the replies. I am suspecting something to do with the Throttle Position Sensor.
Watching the code reader, it is showing strange readings.


Once I saw it showing 45% without the accelerator being pressed and a number of times I have seen it showing 21 or 22 % without the accelerator being pressed.


So I unplugged it, and it idled ok without it plugged in, but a little high about 1000 rpm. The reader showed the code for bad TPS.

[TerryH]

Yeah, there is a filter under there. The pressure kit I got has an adapter, you remove the filter and put the adapter inline and hook gauge to it. The filter has been replaced.

Just a suggestion, and I'm not an expert (where is Rick when you need him), but you said you removed the filter to connect the pressure kit.
To me that means you have only checked FP to a point back of the filter.
Up to and including the fuel rail has not been tested for pressure.
The fuel rail does have a Schrader Valve that you can connect a fuel pressure tester to.
Unfortunately it is under the dog house and may not be easily accessible.
It will, however, give you a pressure reading up to the point of the injectors.
Again, not an expert.

[carl2015]

I'll have to look again, but I didn't see one. But the pressure check there indicates the fuel pump is good. And I am definitely showing some funny readings from the Throttle Position Sensor on the live data with code reader.


Vacuum checked good right around 22, steady reading. Was very slow to bleed off after engine was shut off.


From what I have read on the TPS, it is a likely candidate to cause this problem also. If it shows the accelerator as being depressed, the ECM does not control the idle.

[M & J]

Dont think theres a schrader on the 92 TBI Terry.

[TerryH]

Sorry. Basing it on a 96.
Old age?

[M & J]

Just like me sir.

[Froggy1936]

In my experience with my 95 TBI I suspect the TPS They will do odd things   Frank

[Rickf1985]

Have you cleaned the IAC? If it is hunting due to a dirty Idle air control then the live readings will be all over the place. And being OBDI the readings will be a til behind the actual events. I would try a cleaning before spending money on a new one. Could still be bad but cleaner is cheaper than an IAC.

[M & J]

Is why I said to Google the IAC after FP.

[carl2015]

I do believe the TPS did the trick. I changed it after doing some checking with a meter, let it idle for about 30 mins without the air cleaner on, no problem.
Put air cleaner back on and let it idle for about another 30 mind no problem.


Before changing the TPS it would try to die after about 15 mins.


Thanks for the help and suggestions. This site is a great resource. I'll probably go ahead and pull the IAC off tomorrow and clean it.