I've been having minor issues for some months now where my 2WD 2007 Ranger XLT with 3.0 liter engine and automatic transmission started not wanting to start once it was warm. The first start from cold would crank for a couple of seconds, then start right up. Completely normal. Drive it five miles or more and the second time I wanted it to start it would crank forever without starting. I'd turn it off all the way to where I would be able to remove the key, but instead immediately turn it back to start and it would crank and start within a few seconds... not as fast as the first time but within 5-7 seconds. I could live with that. I had taken it to my usual mechanic but naturally it would run perfectly anytime he was standing in front of it. So I decided to just use it as it was until it became something I couldn't live with.

Late this afternoon, it became something I couldn't live with. I cranked it for the first time of the day (I'm retired and don't have to work) and it started right up... but the idle was fast, like around 2800 rpm fast. I kicked the gas pedal, thinking it would drop down to a slower speed but it immediately started pulsating between full throttle and droping back towards idle ever few seconds. Fast/less fast/fast/less fast ad nauseum. I shut it off.

I waited a minute and cranked it again. Mind you, my foot has not been on the gas during any of the cranking, but it immediately started pulsing fast/less fast until I shut it down after about four cycles of that.

I got in my car and drove to my mechanic's place of business so I would catch him before he closed. I told his front desk guy what was happening and made arrangements for them to send a tow truck to my house on Monday.

When I got home, I tried starting the truck again. It immediately started but it was faster than normal. At least it wasn't pulsating anymore. I eased on the gas and it went up to around 3000 rpm. When I came off the gas it idled at 2500 rpm. If I stepped on the brake for a few seconds, it would slow down the idle to about 1300 rpm until I touched the gas again. Every time I stepped gently on the gas it would accelerate back to around 2800-3000. Now remember, it never ran long enough to come up to a normal temperature. And that pulsation! That was insane.

What is going on with my truck? Anyone have a clue?

 

Remove the brake booster vacuum hose and cap/plug the vacuum port on the intake manifold. Better? Worse? No change?

 

I'm not ignoring your answer. I managed to get the truck out of the garage late Friday and of course it's been raining ever since. Film at 11?

AI also suggested looking at the vacuum booster and the hose going from the intake manifold to it as likely suspects. But I'm going to wait until it stops raining before I do anything. I hate cold rain.

 

What is the fun in that?

 

Yeah, I know, but I'm fully capable of turning a one-hour job into a two-week ordeal. To get soaked on top of that?

So this morning, it's a beautiful day, though a bit breezy and cool. Not a cloud in the sky. I step out to the truck, cross my fingers, and start it up. It cranked a couple of seconds, started right up, and then acted essentially normal. Of course. Fast idle was around 1700 rpm. Slow idle, which I finally saw again for the first time since Thursday, was about 900 rpm.

But what was weird is that every time I stepped on the brake, the rpm would increase about 200 rpm. If I was at fast idle, it idled 200 rpm faster. If I was at slow idle, it idled 200 rpm faster. Very weird.

It doesn't seem to want to do any of the poltergeist stuff today, like wanting to climb to 3000 rpm at idle. Naturally, and of course there are no idiot lights or codes stored. It must know it's going to see the mechanic tomorrow.

As it is, I think I'll take a chance and drop it off up there later today while I can get my neighbor to bring me home. Save myself a tow charge, as long as I don't wreck it on the way.

 

https://www.rockauto.com/en/catalog/...ac)+valve,6072

 

My truck isn't hard to start, nor does it run rough. It's not stalling on me. It just wants to take off with me. I shouldn't have to drive down the road with my foot on the brake for 10 miles. Never adding gas; only adding brake repeatedly as it keeps speeding up on me with my foot completely off the gas pedal, despite a completely flat road. I don't have to accelerate: it does it all by itself.

 

The IAC valve controls idle speed. They can go bad electrically or get gummed up.

Idle speed increase when stepping on the brake pedal is often a sign of a bad booster. A vacuum leak.

If you're responding with what some AI bot overview told you, you're wasting your time. AI is full of crap suggestions. Any crap suggestion that somebody wrote 10 years ago will get regurgitated as "here's your answer".

Good luck.

 

Which is exactly what the OP described so what testing procedure for the IAC lead you to say that is what is needed to fix the problem?

 

I didn't. I pointed to it as something to inspect since it is the primary idle speed control device.

The OP described "no starting problems" and "no stalling", etc. Not sure why. I think that he read an "AI Overview" about problems with the IACV so he's taking that as advice and repeated it back in his post. The AI bots are full of garbage advice.

 

When I clicked on your suggested link, it took me to replacement IAC valves. So the next thing I did was just do a google search on the symptoms of a bad IAC. I saw that my symptoms didn't fit the description of what it said happens when one has a bad IAC.

As Abraham Lincoln once famously said, "The trouble with the internet is you can't believe everything you read on it". Doesn't necessarily make it right. Doesn't necessarily make it wrong either.

I will be driving to the garage in a couple of hours (in my car) so I can explain the symptoms I saw more clearly directly to the guy who is going to be expected to diagnose and correct this problem. If there is a golden lining anywhere, I finally have an issue that is likely to still be there when the truck is at the garage. My last issue, normal crank/start cold (always), followed by long crank/no start (which was worked around by immediately turning off the key, then turning it on to start again, followed by an immediate start) was very intermittent. I took it to the garage and they couldn't get it to do it for them. Intermittent issues are the worst. You can't really fix something you don't see happening.

But this problem is now, and it's happening every time. They should be able to reproduce it, and my hope is they will be able to fix it. Today, preferably.

Whatever happens, you can be confident I will come back and tell you what they found and what they did to correct it. I hate it when I read a thread and when the guy finally gets his problem fixed, he just disappears, so I won't do it to you.

 

Not to be argumentative but your post was a link to a new IAC. There was no advice on how to test/ inspect the part.

EDIT: You didn’t even suggest unplugging the IAC to see if anything changed.

 

Well, this is embarrassing. The mystery is solved. It wasn't a bad brake booster or a vacuum leak. Wasn't a bad IAC. The tech did his thing with his high dollar OBD2 diagnostic tool and it said the throttle was being applied.

Not the throttle cable or anything binding in the engine compartment. Nope, it was my Weathertech floormat. Oops.

In my defense, the Weathertech has a stiff raised lip going all the way around it. I had just taken it out and cleaned it, but didn't put one and one together to even think to look at the floorboard. I've had that floormat for years and never had it interfere with the gas pedal before.

Man, am I glad I didn't have it towed up there this morning. As it was, I did get them to check my brakes which are apparently OK. My education ran me right at $80 and some embarrassment.

I told you I would share the outcome, whatever it was. So, enjoy my lesson and file this little tidbit of knowledge away because one day it might be you. I've been driving for more than half a century and never had this happen to me before. I have now.

But like I said, "Oops".

 

my '91 2.3l idles at 1400. New sensors everywhere to no avail. The TPS is most of my issue as it is above 1.0v at idle. Ive slotted the sensor to get some adjustment and it isn't enough. Unplug the Mass Air next time it goes high and see if that changes things.