How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask david craig Your Own Question
david craig
david craig, Auto Mechanic
Category: Volvo
Satisfied Customers: 3565
Experience:  owner/mechanic at 3D Automotive
4993992
Type Your Volvo Question Here...
david craig is online now
A new question is answered every 9 seconds

Very strange.... it has erratic and dangerous idle

Customer Question

very strange.... it has erratic and dangerous idle situation. Stopped at a stop sign, foot on the brake and the idle jumps from 800 to 1500, but the car lurches forward.
JA: How many miles are on the car? What size is the engine?
Customer: 187,000, 2001, s40 with 1.9 turbo
JA: What year is your Turbo?
Customer: 2001
JA: Are you fixing your Turbo yourself? What have you tried so far?
Customer: I removed the fuel pressure regulator and found that the screen was damaged, so I bought a new regulator. I got a junk yard idle air control valve. I was able to mechanically test my valve and the JY one. Both seemed to do the same thing. several months back I cleaned the MAF and TB. I fugured I would do that again today.
JA: Anything else you want the mechanic to know before I connect you?
Customer: erratic idle that lurches the car forward. It also happens when coasting down a hill... the acceleration is fast enough for the tranz to change gears.
Submitted: 1 year ago.
Category: Volvo
Expert:  david craig replied 1 year ago.

Hi Im David, thanks for visiting the site. please allow me to look some information up on your vehicle. thanks

Expert:  david craig replied 1 year ago.

It appears to me to be an issue with the throttle position sensor or the accelerator pedal position sensor. to test the throttle position sensor, connect an volt meter to the sensors connector and manually operation the throttle plate. closed voltage should read around .4-.5 vdc and smoothly increase to 4.5-5.0vdc as you manually open the throttle plate.

Customer: replied 1 year ago.
Ok, I am having trouble disconnecting the TB sensor. But once I do, what position is the key in?
Expert:  david craig replied 1 year ago.

you can leave the key off for now

Customer: replied 1 year ago.
had to take the TB off to see how the connector attached. there are 3 connections.... which do I check....
Expert:  david craig replied 1 year ago.

the one on the right

Customer: replied 1 year ago.
Ok. I am checking the TB connections. Not the wire?
Customer: replied 1 year ago.
Red Voltmeter wire on the right male connection. Black VM to ground?
Expert:  david craig replied 1 year ago.

not the wire. how many pins are on the sensor?

Customer: replied 1 year ago.
How do i get voltage with the connector dis connected
Customer: replied 1 year ago.
3
Expert:  david craig replied 1 year ago.

i wanted you to disconnect the sensor to see if it was corroded inside. sorry i should have explained that. with the connector installed you need to back probe with the meter

Customer: replied 1 year ago.
Makes sense now. I'll work on that. I see no corrosion.
Customer: replied 1 year ago.
3 wires. Red, brown and green. Which ones?
Expert:  david craig replied 1 year ago.

standby please. let me get you a print

Expert:  david craig replied 1 year ago.

heres a video. a lot easier than explaining.

https://youtu.be/m_6dhZzWM54

Customer: replied 1 year ago.
Using my phone invthe driveway. Kinda tuff to waych a vid. Just need to know th 2 wire colors.
Expert:  david craig replied 1 year ago.

the 2 end wires

Customer: replied 1 year ago.
Ok. Key still off?
Expert:  david craig replied 1 year ago.

yes

Customer: replied 1 year ago.
1st try i got .04v closed(idle). Open the throttle and it went to 0v. Get no readings now. Re checked continuity but still get 0v
Expert:  david craig replied 1 year ago.

make sure you have the probes in far enough

Customer: replied 1 year ago.
I got continuity from the probe to the connector. Using the same back probe method, Should i get voltage on the center wire? Cause i don't.
Expert:  david craig replied 1 year ago.

no. thats the input from the ecm

Expert:  david craig replied 1 year ago.

you might get it with the key on

Customer: replied 1 year ago.
OK
Customer: replied 1 year ago.
5v with key on. Center wire
Expert:  david craig replied 1 year ago.

thats good

Customer: replied 1 year ago.
5v on other probes with key on and TB closed.
Customer: replied 1 year ago.
Up to 5v wot.
Expert:  david craig replied 1 year ago.

ok then my bad. the key should have been on. sorry bout that

Expert:  david craig replied 1 year ago.

so the tps is good.

Customer: replied 1 year ago.
the key needs to be on.
Expert:  david craig replied 1 year ago.

it was the resistance check that the key was to be off

Customer: replied 1 year ago.
My thoughts too.
Expert:  david craig replied 1 year ago.

but thats not necessary since the voltage is good

Expert:  david craig replied 1 year ago.

do a wiggle test with the meter still hooked up.

Expert:  david craig replied 1 year ago.

see if vibration affects the reading

Customer: replied 1 year ago.
wigggle what?
Expert:  david craig replied 1 year ago.

the wiring harness that the sensors connector is in.

Customer: replied 1 year ago.
It did. But could that be my probe cpnnections?
Expert:  david craig replied 1 year ago.

sure could be. another way to check would be to start the vehicle and shake the harness. see if it affects the rpms

Customer: replied 1 year ago.
I do get some drop.
Customer: replied 1 year ago.
I can't reach the connector with everything attached.
Expert:  david craig replied 1 year ago.

do you have a scan tool?

Customer: replied 1 year ago.
Just grabbing the connector and wiggling gives no drop.
Customer: replied 1 year ago.
OBD? Yes
Expert:  david craig replied 1 year ago.

ok. wiring is probably ok

Expert:  david craig replied 1 year ago.

yes obd. does it read live data?

Customer: replied 1 year ago.
No just codes.
Expert:  david craig replied 1 year ago.

and the check engine light is not on correct?

Customer: replied 1 year ago.
Correct. I'll put it all back together and see if anything is pending.
Expert:  david craig replied 1 year ago.

ok. and i will pull a a test for the accelerator pedal position sensor if i can find one in my books

Customer: replied 1 year ago.
No codes, none pending.
Expert:  david craig replied 1 year ago.

ok the best way to test the accelerator pedal position sensor is to start the vehicle. let it get to operating temp. then slowly and steadily accelerate at from idle to 3000 rpms. the rpms should go up smoothly with out any dead spots or rapid rpm changes

Customer: replied 1 year ago.
Ok
Customer: replied 1 year ago.
5 or 6 tries. Most were smooth. 1 the rpm took off by itself to 4500. Now i am siting here typing and it dis it again.
Expert:  david craig replied 1 year ago.

replace the pedal position sensor.

Customer: replied 1 year ago.
again. Up to 4000. Hold for a sec then down to 800 and holds.
Customer: replied 1 year ago.
where is that?
Expert:  david craig replied 1 year ago.

it is attaches to the gas pedal assembly on top of it

Expert:  david craig replied 1 year ago.

i believe its all one piece

Customer: replied 1 year ago.
Ok. How do i keep you in the loop? I assume this is something i'll have to get on line. I can try a jy one.
Customer: replied 1 year ago.
Looks easy enough.
Expert:  david craig replied 1 year ago.

you can accept the answer, leave a 5 star rating and i will keep this open until we get her fixed.

Customer: replied 1 year ago.
Mine looks different. There is a rod connecting the pedal to the hinge. Pedal forward pushes down on a vacuum can. 2001 S40 b
Expert:  david craig replied 1 year ago.

ok, yea i saw that one too. let me pull something up

Customer: replied 1 year ago.
Not aure about the vacuum can. Does not seem to touch it. Hose on top, hose on bottom. It is just mounted on the same bracket as the pedal.
Expert:  david craig replied 1 year ago.

yea, the pic i sent is the only thing i can find

Customer: replied 1 year ago.
Do i have a pedal position sendor?
Expert:  david craig replied 1 year ago.

can you take a pic of the pedal assembly area

Expert:  david craig replied 1 year ago.

according to my manual you do...sorry the pic is so small

Customer: replied 1 year ago.
Found one on ebay.
Expert:  david craig replied 1 year ago.

there you go. good find

Expert:  david craig replied 1 year ago.

im confident that with that erratic behavior, especially while you were testing it, that will take care of your issue.

Customer: replied 1 year ago.
The whole thing? I just dont see a sensor. I can't read the part # in the picture.
Expert:  david craig replied 1 year ago.

i have to do some more research

Customer: replied 1 year ago.
Thanks for your help.
Expert:  david craig replied 1 year ago.

sorry, had to run out for a few, let me get the coffee started......

Customer: replied 1 year ago.
No rush. Had another car to fix. Beer and football is on the list for the night. Let me know the next thoughts and i'll be on it.…tomorrow ��
Expert:  david craig replied 1 year ago.

ok brother

Customer: replied 1 year ago.
I'll have some time to fiddle with the S40 after 4pm today. Did you come up with any more thoughts. I searched the internet for a 2001 Accelerator Pedal Position sensor and don't seem to find one. Do you have a part #?
Expert:  david craig replied 1 year ago.

im going to call the local volvo dealer

Expert:  david craig replied 1 year ago.

last 8 of you vin?

Customer: replied 1 year ago.
great. I thought I would drive the car to dinner Saturday. WOW>>> it used to rev to 1500 at a stop sign, now the 4000 rev is much more frequent. I turned around and changed cars. Not driving that one 'til we can calm it down a bit. This is my daughters car, she is surely not driving it.
Customer: replied 1 year ago.
4176 is the last 4. I have the whole thing if you need it.
Expert:  david craig replied 1 year ago.

the last 8

Customer: replied 1 year ago.
1F714176
Expert:  david craig replied 1 year ago.

let me have the whole thing...sorry

Expert:  david craig replied 1 year ago.

you dont have one on the vehicle.

Expert:  david craig replied 1 year ago.

it only work by the throttle cable which connects to the throttle linkage on the side of the throttle body. so i have to suspect the tps is bad/intermittent

Customer: replied 1 year ago.
If you still need it.TV1VS9501F714176
Customer: replied 1 year ago.
The yard that i got the IAC from has a TB. I'll see if he will trade. I think it is from a 2000. I'll look for a new one too.
Customer: replied 1 year ago.
Question for you...
1. the TB valve is mechanical and operated by my foot
2. Fuel injection cars are controlled with AIR intake. More air mixes with more fuel and the engine revs, right?
??? So how is more air randomly getting into the intake to rev my car to 4000 rpm? The TB plate is not opening. Even if the computer thought it was open there would not be more air.
Expert:  david craig replied 1 year ago.

vacuum leak

Expert:  david craig replied 1 year ago.

unmetered air entering the engine after the maf sensor

Customer: replied 1 year ago.
A new (different) TB would not solve a vacuum leak tho. the current TB gasket is new and whole.
Expert:  david craig replied 1 year ago.

you can have a vacuum leak anywhere. intake manifold base, ant vacuum hose, brake booster, etc....

Expert:  david craig replied 1 year ago.

get a can of throttle body cleaner and spray all around the engine at any all all sources of vavcuum. if the rpms rev. you have found a leak. but im putting my money on tps

Customer: replied 1 year ago.
i'll get the JY one on the way home. The guy is very nice and will refund my $ if it does not solve my issue. I have the IAC valve to return to him any way.... but I forgot to bring it today. I have tried the carb spray all around the TB, intake, MAF etc... I have never found a vacuum leak on any car.... I hate vacuum leaks. I may as well try it again tho.
Expert:  david craig replied 1 year ago.

ok my friend. keep me posted

Customer: replied 1 year ago.
I got the TB. Gonna need some cleaning. JY dude did not want me to remove the sensor but i might anyway. The thing is a mess.
Expert:  david craig replied 1 year ago.

do it

Customer: replied 1 year ago.
Totally worse now 5 minute test drive was good. At 6th minute crap hit the fan. High revs all the time. I made it home but now it won't start.
Expert:  david craig replied 1 year ago.

what codes you have?

Customer: replied 1 year ago.
No cel
Expert:  david craig replied 1 year ago.

what? ok. can you monitor live data?

Customer: replied 1 year ago.
No check engine light. Only have obd reader.
Expert:  david craig replied 1 year ago.

ok. let me go back over our notes..ill get back with ya

Customer: replied 1 year ago.
I may have found it. The brake booster has a hard plastic pipe that inserts between the TB and the intake. The end of the pipe has a smooth brass nipple that inserts into a wedge type fastener. That connection was wobbly and slid up and down easily. I was able to get it out. Inside the wedge connector is or was an o-ring. Mine is brittle and broken. I suppose as the engine warms up the metal expands and reveals the leak.Looking for an oring to try this afternoon.
Expert:  david craig replied 1 year ago.

nice find and will definitely cause a vac leak

Customer: replied 1 year ago.
I am trying to find a drawing of that area. I can find the hose, but it does not come with the press-to-lock connector or the O-ring.
Since my O-ring broke into pieces, I am not sure what the size specs are.Do you suppose a regular O-ring will be fine to use? I found several at work we use for hydraulics. Orielly's has O-rings for oil and a pack of O-rings made from Viton for gas. This area is near the fuel intake, but it is really only hot air near this O-ring.
Expert:  david craig replied 1 year ago.

if you want to be sure its not going to leak i suggest the dealer parts

Customer: replied 1 year ago.
the damn dealer does not answer the phone. they only communicate with customers at the desk, or online. I emailed them, but who knows how long or if they will ever reply.
Customer: replied 1 year ago.
I have to return these JY parts, so I think I will see if my Junk Yard guy will let me back in the yard. If for nothing else, I can get the press-to-lock and maybe a complete o-ring, but it will probably be brittle too.
Expert:  david craig replied 1 year ago.

how far away is it? drive on down there. walk into the parts department and tell the knucklehead what part you need. dont but jy...especially that

Customer: replied 1 year ago.
I was just thinking the JY for size. There are 2 dealers in town, one is 30 minutes away. They are the pricks. then there is Darrel Waltrip 45 to 50 minutes away. If I have found the right parts online, it won't be $13 for the connector and the o-ring. Just hate to drive that far and them not have it.I am gonna try to use these tonight. Get a good test drive in, maybe drive the car to work tomorrow (fingers crossed), then deal with the correct part.
Expert:  david craig replied 1 year ago.

okey dokey

Customer: replied 1 year ago.
Hey, I got an email reply. I asked him to lookup this part #(###) ###-#### and tell me if there is an oring inside the piece on the left. piece on the right is labeled a plug. I don't want to plug it.http://www.tascaparts.com/oe-volvo/9146615
Expert:  david craig replied 1 year ago.

so what are you gonna do?

Customer: replied 1 year ago.
Bout to go on a test drive.
Expert:  david craig replied 1 year ago.

HOPE ITS A GOOD ONE

Customer: replied 1 year ago.
I thought it was. Got greedy after10 minutes. Then it started over revving again. And like yesterday the car won't start. Guess it flooded when i shut down at 4500 rpm.
Customer: replied 1 year ago.
Problem is now. I am not to close to home.
Expert:  david craig replied 1 year ago.

dude that tps has got to be bad!!!!!!! that or the damn cables ae sticking or the bracket for the throttle cable is on wrong

Expert:  david craig replied 1 year ago.

hows it going?

Customer: replied 1 year ago.
I finally gave up. I found an independent shop that says they specialize in Volvo. The owner was a dealer mechanic. I figured they would have the diagnostic equipment to pin-point my problem. The place is 20 miles from my house, so I was leary about being able to make it. But I babied the car all the way there. When I pulled in and parked the revs hit 3000 and would not stop. I turned it off and put the key in the drop box.They called and told me the following, what do you think?: During their test drive the battery died and would not charge via the ALT, or with a charger. They took the battery out of the car and the charger charged the battery. Then they put the battery back and got wild voltage #s throughout the system.1. they determined that the ALT was shot (under warranty, so that part will be covered)
2. they tell me the + batt cable goes thru or under the intake manifold and has a short in it.
3. Intake mani. has to come off to get the cable out and will need a new gasket.I am having trouble believing that the +batt cable could be causing this, but I suppose with all the sensors and computers in cars these days it could be the problem.How would the car REV assuming there are no vacuum leaks and the Throttle valve is not opening? How is it able to rev? wouldn't MORE AIR have to be introduced to make it rev?Dumb founded.....
Expert:  david craig replied 1 year ago.

unless the cable being shorted causing all the sensors to go nuts..............

Customer: replied 1 year ago.
I asked them to show me the cable when they pull it.
Expert:  david craig replied 1 year ago.

unless they purposely damage it.