High RPM when hit a paving road hole only

jazzkramer · Jul 5, 2016

Hi guys,
I've read all possible thread on the internet about high Idle.

No one seems to have my problem.

I drive a 1996 Ford Ranger 2.3L, it's "almost perfect" (not true,

but....)

I'm italian but I live in Dominican Republic, where the paving road is full
of deep holes.

Every time I drive over a hole and the truck receives a hit from it,
the idle rpm go to 3000 for a while (if I press the clutch for example at a traffic light or stop).
It slowly goes down to normal...
BUT it ONLY happens after I "hit" a street hole.

I tried, when parked with engine runnig, to hit or moove many parts of the engine, contacts, sensors, wires, to find the guilty one... but I can not replicate the problem myself... and...
when driving it's impossible to check inside the engine what is happening.

Any ideas?

Thank you,
Alberto.

RonD · Jul 5, 2016

Reads like a vacuum leak.

Check PCV valve, with engine idling pull the PCV hose off the intake manifold and see if idle shoots up to 3,000 or so.

Inside PCV valve is a weight, the thing you can hear rattling when you shake it.
At idle the engine vacuum should hold that weight in place so no vacuum leak, at higher RPMs, low vacuum, weight is lowered so Blow-by can be sucked out of the engine.
If you hit a bump hard enough that weight could drop, opening up the PCV hose and sending RPMs up.

tomw · Jul 6, 2016

How about an IAC that gets 'jammed' by the impact? I doubt a person could whack an IAC as much as the engine thumping around after a pot hole. Can't hurt to remove it, inspect for carbon deposits that could be causing it to respond more slowly than normal. Clean with carburetor cleaner (check that residual fumes cannot damage the O2 sensor) and re-install. Disconnect the battery for a while to let the idle get re-learned on startup.
tom

jazzkramer · Jul 7, 2016

Thanks Ron and Tom for your fast replies,
I will try both things to check if I can solve.
I will let you know. I think I will have time this Saturday
(I hope no rain because I have no garage

).

Thank you for your help.

Alberto.

jazzkramer · Jul 8, 2016

Hi guys, I actually had time today to very well clean the IAC and find the PCV valve.

Moving the PCV valve there something moving inside so it's not stuck. (Maybe I will change it, I sow it's 5 dollars).
I had not the time to disconnect it from the hose but I could just pull very simply from the engine hole it was in. It seems it does not has any fixing in the engine.. is it correct?

I had the opportunity to check the computer errors and it said "P1506"
that is:
- Faulty Idle Air Control (IAC) valve
- IAC valve harness is open or shorted
- IAC valve circuit poor electrical connection
- Intake leaks
- Stuck PCV Valve

and
and P500.. Yes I have the speed sensor in differential broken, but I don't think this is the cause of the problem becouse it's broken since I bougth the truck, and it had no problems at that time.

SO: After checking the valves,
I cleaned errors codes and took it for a small ride: on small street bump was ok (so it's better than before) but on a big hole it had the problem again.
I re-checked the errors and no errors at the moment. Maybe the computer needs time before adding an error.

So I have to better check both valves (PCV and IAC).
Electric contacts...
Intake Leaks...

Hope I solve!!

Thanks for help!

Alberto.

tomw · Jul 9, 2016

The PCV(positive crankcase ventilation) valves sold in the aftermarket will come with a fitting for vacuum lines.(the ones I have seen look like a letter "F") You do not need the fitting, but it may make you think you are being given the wrong part. The valve fits 'inline', stuffed into hoses on either end. There are no clamps or retainers other than friction to hold it in place.
The codes listed seem to indicate the IAC wires/wiring may have problems or the IAC is not responding to computer commands. From the 'bump' theory, I would be inspecting the wire looms and connections for the IAC. You might give a tug to the individual wires in the IAC connector to determine if they are tightly connected to the lugs of the IAC connector. Sometimes the plastic gets old and 'loose', allowing the internal connectors to avoid connecting as they can relax backwards when the connection is made.
tom

jazzkramer · Jul 9, 2016

Thanks Tom,
I think I found the "only one hose version" of the PCV, it's like the old one I have in the truck, it's an L not an F

.
Thanks for the explicaiton of no retainer, and the hose look good, so I will remove a possible cause of the problem.

For the IAC thing, tomorrow I will check the wires and the connections to the IAC. It could be that when bumping, the connection get lose...

Thanks, going on with others urgent maintenance... like BRAKES.
(...and today I just discover I have the wrong Brake Adjuster for the back drum brake it's for 9" but my truck has 10" :sad:

...already bought the correct one. Hope it's coming fast!)

Thank you, I will tell you about the IAC contact think,

Alberto.

tomw · Jul 10, 2016

Some of the adapters that get stuffed into the outlet of the PCV valve have two vacuum lines. I do not know the application, but think it was the mid-to-late 1970's. They've been using this thing for a while now...
If the adjuster you refer to is the threaded assembly at the bottom of the brakes, connecting the two brake shoes, a 9" can work in a 10" if it is extended a bit, but when the shoes wear, it may unscrew completely and come apart. Not good.
tom

jazzkramer · Jul 26, 2016

Hi, sorry to be so late with my reply.... I was away...

SOLVED!!

(I also got a wrong brake adjuster... the 9".... yes, it does not fit good my 10"...
Than got the correct one and I solved. The problem wasn't the part Tomw refers, they are actually the same in 9" or 10",
but the small metal wire connecting from top to botton that make the adjust screw turn, the 9" one is too short for the 10")

I thank you all for the "bump rpm" problems.

I actually don't know the guilty thing, but I replaced the IAC valve and its connector and the PCV valve.
I make sure the connector can not be pulled by other wires in a "street bump".

I drove about 500 km and the problem seems to be gone,
Thanks guys!!! :beer:

The normal idle also seems to be lower and stable.

I will have some others small fix to do (I think I have a broken O2 sensor wire under the vehicle), but eventually I will open a specific thread in case of problems.

Bye, again thanks, Alberto.

RonD · Jul 26, 2016

Thanks for the update, good work :icon_thumby:

tomw · Jul 27, 2016

Good to hear you seem to have the problems fixed.
I did not know the two adjusters were the same dimension. Guess it makes sense as all they do is slowly un-screw, and the shoe dimension could change without any problem. Good to know.
From what I have read, the pre- and post converter O2 sensors in many vehicles are the same functionally, they just have different lengths of wire to accommodate their position. Some aftermarket do not have 'factory' style connectors, but are supplied with 'butt' connectors and shrink-wrap insulators. You use the old connector, and splice the new O2 to it.
tom

High RPM when hit a paving road hole only

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