Hi all, great forum we have here! Learned a lot from all the posts.

This question is in regard to a 2001 Expy Eddie B, big engine, with about 50,000 miles. All service has been done by me, pretty much on schedule.

The truck is used as a daily driver and usually not worked hard.

Recently when starting for the first time after sitting all night, the idle immediately goes to about 1600 RPM and then after I put my foot on the gas pedal, [I think that's what I do] the idle drops down to around 700 or what seems like normal.

The rest of the day everything is fine.

Oil was changed abt 4000 miles ago, mass air flow sensor was sprayed then IIRC, new fuel filter when the book called for it, air cleaner was changed last oil change or the change before. Running Mobile-1 5-20.

Haven't started to diagnose the problem yet, wanted to hear some ideas from the knowlegable folks here first. [Have some ideas tho...]

I'll give thorough feedback WRT the diagnosis and repair.

 

I will suggest four things that will cause a too high idle when first started.

1: Engine temp sensor is out of range and thinks the engine is colder than it actually is, causing higher start up rpm and a richer condition.

2: Throttle position sensor is set a little too high, meaning back probed voltage KOEO is above 1.0 volts. The voltage should be between .95 -.98. Very easy fix.

3: Vacuum leak, most likely at pre-formed elbow that exits from the back of the intake that leads to the PCV valve .

4: IAC valve, but check free stuff first before replacing. Usually the IAC won't let the engine idle high enough or causes surges.

 

Thank you Yardbird.

Could you tell me or direct me where to find the steps to check and adjust the TPS voltage?

Don't have a Chilton here, it's at home.

ETA, 2000 miles away.

 

Assuming that the TPS has not been changed, and was set correctly at the factory,(not always the case), the voltages should not be out of range. If the throttle stop has been adjusted then you would have a concern.

I will look tomorrow on mine and give you the correct wires to back probe(if I don't get called into work early, which has happened a lot lately).

 

Look forward to it!

 

Over the 5+ years I've owned my Expy, this topic has come up countless times. The consensus among most, including several service techs, is it's normal and nothing to worry about...mine's been doing it since day one and it doesn't bother me.

 

I did several searches and couldn't find anything on this recently.

Just started it warm and it went to 1500 RPM and immediately dropped to idle, earlier when cold it went to 1700 and stayed there a few seconds longer before going to idle.

I can't imagine reving so fast cold is good for cylinder walls, bearings etc before oil starts circulating.

There is a lot of "normal" engine "clatter" when starting cold and the engine revs high.

I'll be doing maintainance and diagnostics in a few days.

 

^ This is the EXACT behavior seen by many of us.

 

i would think if it is dropping in a few seconds it would not be too bad never thought anything of it here.

 

Mine revs to about the same level (~1700rpm) for a few seconds after a cold start and then drops to a more reasonable level (~1000rpm). All the service techs and engine guru's tell me that this is for emissions purposes and it is programmed into the engine computer and CANNOT be changed.

 

I finally was able to ckeck which wire to test on the TPS.

You will need to backprobe the center wire using a pin or needle in order to make contact. Touch the red wire to the needle and ground the black with your ohm meter.

I checked mine and it is out of range with a 1.06 volt reading, but my engine never revs above 1200 rpm, so I think I will leave the TPS alone for now.

Sorry for the delay. I have been waking up and going to work, and then getting home after midnight.

 

Our '00 Expy 5.4 with 43K mi. does exactly the the same thing on cold starts and it is normal. We tow a heavy trailer regularly and change oil every 4-5k miles and it uses just a tad btwn. changes. Unless you are experiencing something new to your Expy (versus you driving it on vacation when your wife normaly drives it ), I'd put it behind you as they all do it... (by the way, DON'T touch the throttle, let it slow down on it's own)

A friend of mine that was a new owner (of a used Expy) took theirs in to a dealer because of the cold start rev'ing. A kilo-buck later and it still does the same thing and the dealer now said it's normal. Too bad they called me after the fact to see what ours did on cold start...

Enjoy the Expy, it's a great truck, one that Chevy wished they could figure out how to build!

 

Yardbird, I checked the TPS just now.

For others, it's located on the right side of the throttle body asm. There are 3 wires coming out of it facing the front of the truck.

The top wire is regulated 5VDC from the computer, the second wire is the sensor output and that is the wire you probe with a sharp pointed dental tool-like probe. It is a pretty thin insulated wire so don't mess it up with a large probe like on a continuity tester or something.

My sensor output is reading .98 VDC Kon/Eoff and you say that is normal.

A little more info, on a hunch, the first thing I did to diagnose the "racing" idle on start was to pull the PCV valve. Blowing and sucking thru it proved it was contaminated. I could blow into the top and there was significant restriction and shaking it caused the restriction to vary. So I replaced it.

The milage around town had been indicating 11.3MPG and that's lower than usual. Afterward putting in the new PCV and resetting the computer, I'm seeing about 13MPG. That's after a dozen or more start cycles and 2 days around town driving.

My other expy, same engine, year and model gets about 14MPG at sea level elevation, it's on the east coast. Here, this one is about 4500 elev. The east coast one doesn't do the over reving thing on start, that's why I believed this truck had a problem, notwithstanding the comments of others that aggressive start idle is normal.

After installing the new PCV valve the engine idle at start is a lot less aggressive, about 1500RPM and it doesn't sound like the truck is trying to launch into space.

Still have some work to do to it, oil and tranny oil chg [just 6 qts for the tranny each oil chg], clean the mass air sensor, new air filter, etc.

Just replaced the battery with one from Sams. BTW, the old battery from Sams in 2002 weighed 47lbs, had a CCA of 1000.

The new one they're selling weighs 42# and has a CCA of ~800, so Sams is selling a weaker battery for some reason.

 

Don't think there's anything wrong. I have two fords, one an expy and they both do it. I'll start one from an overnight sit, the rpm's will stay at about 1500 for a short time and then drop down to normal. Actually if I remeber correctly every car I've owned does that. I must be misunderstanded the problem.