why is my engine racing ?

M

mabo

Club Member
Nov 13, 2011
5,365
5,007
south wales
My v6 has been largely unused for the last few years. During it's partial hibernation I have;
Fitted St 200 airbox
ST 200 throttle body
Modified the bracket to accept the appropriate throttle cable to match the throttle body.
Changed the exhaust system to a twin outlet type.
Changed the exhaust manifolds to tubular type thereby removing the two lead cats and the pipe that links the rear exhaust manifold to the inlet manifold.
Blanked off and removed the EGR valve as it is now redundant.
The main cat is still installed.
The vast majority of the components have been sourced from your good selves
The car is now in use and during the off time and changes has developed an annoying problem in that the engine often race up to 3k, typically when I slow down and move to a lower gear to park.
I'm pretty sure it's doing something similar on the motorway, it just doesn't slow down as much as it used to when I throttle off, I'm braking a lot more than I used to.
I fitted new gaskets on the inlet manifold, nor does it sound as if it's sucking in air around the inlet manifold.
I imagine maybe some sensor has failed on the injection system, the lambda sensors have effectively been changed as I left the used ones in the tubular manifolds that came with them but so far as I know they would not control the fuel mixture to that degree.
Anyone else had this problem after similar conversion ? Thanks in anticipation, Mabo.
 
Thanks guys, All in need to do now is figure our for sure where these things are. IACV with black cap on the rear of the manifold ?
TPS on the throttle body ?
 
IACV is in that area but is fitted horizontally; silver canister held on with two bolts, electric plug on end facing passenger side.
TPS is on the throttle body.
 
Quicksilver said:
IACV is in that area but is fitted horizontally; silver canister held on with two bolts, electric plug on end facing passenger side.
TPS is on the throttle body.
Click to expand...

Googling about it sounds more likely to be the IACV which also looks like the easier fix so I'll have a play over the weekend. I wonder if I transferred it across from my old manifold, it was a while back I did the swop. Either way I'll whip it off and clean her out.
wait for the update ! Thanks again guys.
 
You may have already checked this but you say you've modified the throttle cable bracket.. have u checked that the cable isnt sticking or is slow to return ,could it be holding the throttle open slightly when in rest position...

If you fitted an st throttle body could that be sticking...is the adjustable stop bolt set correctly.

Just some ideas to check if u haven't already
 
shirtyzeus said:
You may have already checked this but you say you've modified the throttle cable bracket.. have u checked that the cable isnt sticking or is slow to return ,could it be holding the throttle open slightly when in rest position...

If you fitted an st throttle body could that be sticking...is the adjustable stop bolt set correctly.

Just some ideas to check if u haven't already
Click to expand...

Agreed. Start it with the throttle cable (and CC cable if fitted) disconnected. If you used standard parts that shouldn't be the problem, but it's a simple test you can do without spending money.

My bet is that the engine will still race. Money is on Manos and Tony being right. A sticking IACV is likely.

And if not, move on to Paul's advice. A faulty MAF will do really weird stuff.

:edit: Another thought. If it idles okay but high, check the state of your bellows (behind the MAF) and also the crankcase breathers. You might be getting air from somewhere that the car isn't expecting it, and after where it is metered.
 
Mako said:
Agreed. Start it with the throttle cable (and CC cable if fitted) disconnected. If you used standard parts that shouldn't be the problem, but it's a simple test you can do without spending money.

My bet is that the engine will still race. Money is on Manos and Tony being right. A sticking IACV is likely.

And if not, move on to Paul's advice. A faulty MAF will do really weird stuff.

:edit: Another thought. If it idles okay but high, check the state of your bellows (behind the MAF) and also the crankcase breathers. You might be getting air from somewhere that the car isn't expecting it, and after where it is metered.
Click to expand...
IACV would be my first port of call, MAF is easy to check, if its working and you disconnect it with the engine running the idle will go lumpy
 
This sounds like the IACV to me as well. I had the same problem when I fitted Dave's UIM that came with one fitted. Engine would just sit on and above 3000 revs. I swapped the one over from my UIM and it solved it straight away.
 
shirtyzeus said:
You may have already checked this but you say you've modified the throttle cable bracket.. have u checked that the cable isnt sticking or is slow to return ,could it be holding the throttle open slightly when in rest position...

If you fitted an st throttle body could that be sticking...is the adjustable stop bolt set correctly.

Just some ideas to check if u haven't already
Click to expand...
I've had similar thoughts but my bracket is perfectly aligned, its the original with a relocated hole cut at the correct location and a third leg added to keep it all square, You have to look close to spot it's not original because mostly it is. The cable is a new ford item, all be it sourced via Ebay.
No CC cable to worry about. The throttle stop screw seems to be OK, She will settle down to a nice tickover but often races up to 3K first before dying back. Today on the way home I could throttle off at 65 / 70 and on the slight down hill she doesn't slow at all.
 
Last edited:
Over the weekend I removed the IACV and filled it brake cleaner fluid. It didn't seem to have any significant effect so I decided I wanted to dismantle it.
First problem is to separate the valve from the solenoid, ie the elec bit from the mechanical bit. They are held together using a crimped or folded flange on the end of the solenoid. With a fair bit of vandalism I was able to prise the flange back using hammer screwdriver and a vice.
The two components could then be pulled manouvered apart. The moving part of the valve could then be removed, I cleaned the moving shaft with some wet and dry paper, I stretched the spring a little too to refresh it after 15 or so years of service. I tested it by blowing through it with the valve open and closed and all seemed well. With the whole lot reassembled I put it back on the car and started her up, she was racing a little as the engine was cold so it would be calling for choke. I unplugged the electrical connection and the revs dropped to an appropriate level. I drove her around the block still with the electrical connection off to warm her up. Back home I plugged the elec connection back on and the revs went up again. So I decided to leave it disconnected.
She started OK this morning and I did my work journey with a normal driving experience. When I arrived an hour later the engine was up to temp. Reconnecting the elec to the unit caused the revs to rise very slightly but not enough to see any difference on the rev counter. I left it disconnected but it seemed to be doing the right thing.
Coming home she was a little more reluctant to stay running after she started, she cut out once or twice before I pulled away but a little bit of heel and toe let me get out onto the main road and away. We came home without event and she was back to her old self.
I've left the elec connection off and we'll see what happens tomorrow. Might be a bonus, might be me being gentle but the average fuel consumption crept up by 1 MPG over the day but that might be because I wasn't giving her the beans away from roundabouts to enjoy the exhaust note as I was on the way home on Friday.
As the valve seems to be performing normally and I'll only know for sure when I plug it back in, I am wondering about whatever device monitors the engine temperature to decide if it wants choke or not, is it generating an incorrect signal. If it is then surely I'd have the racing caused by the valve even though the valve is ok. What do you guys think ?
Or have I misinterpreted the purpose of the IACV.
 
Last edited:
mabo said:
Now that's exactly the sort of intelligent answer I'd expect from you. Thankyou for reading through my lengthy post !
Click to expand...

I can't claim to be intelligent. But don't run the car without the IACV connected for any length of time.

Also, if you use wet-and-dry on moving faces, please make sure you clean them thoroughly.
 
mabo said:
Over the weekend I removed the IACV and filled it brake cleaner fluid. It didn't seem to have any significant effect so I decided I wanted to dismantle it.
First problem is to separate the valve from the solenoid, ie the elec bit from the mechanical bit. They are held together using a crimped or folded flange on the end of the solenoid. With a fair bit of vandalism I was able to prise the flange back using hammer screwdriver and a vice.
The two components could then be pulled manouvered apart. The moving part of the valve could then be removed, I cleaned the moving shaft with some wet and dry paper, I stretched the spring a little too to refresh it after 15 or so years of service. I tested it by blowing through it with the valve open and closed and all seemed well. With the whole lot reassembled I put it back on the car and started her up, she was racing a little as the engine was cold so it would be calling for choke. I unplugged the electrical connection and the revs dropped to an appropriate level. I drove her around the block still with the electrical connection off to warm her up. Back home I plugged the elec connection back on and the revs went up again. So I decided to leave it disconnected.
She started OK this morning and I did my work journey with a normal driving experience. When I arrived an hour later the engine was up to temp. Reconnecting the elec to the unit caused the revs to rise very slightly but not enough to see any difference on the rev counter. I left it disconnected but it seemed to be doing the right thing.
Coming home she was a little more reluctant to stay running after she started, she cut out once or twice before I pulled away but a little bit of heel and toe let me get out onto the main road and away. We came home without event and she was back to her old self.
I've left the elec connection off and we'll see what happens tomorrow. Might be a bonus, might be me being gentle but the average fuel consumption crept up by 1 MPG over the day but that might be because I wasn't giving her the beans away from roundabouts to enjoy the exhaust note as I was on the way home on Friday.
As the valve seems to be performing normally and I'll only know for sure when I plug it back in, I am wondering about whatever device monitors the engine temperature to decide if it wants choke or not, is it generating an incorrect signal. If it is then surely I'd have the racing caused by the valve even though the valve is ok. What do you guys think ?
Or have I misinterpreted the purpose of the IACV.
Click to expand...
https://en.wikipedia.org/wiki/Idle_air_control_actuator
 
Mako said:
I can't claim to be intelligent. But don't run the car without the IACV connected for any length of time.

Also, if you use wet-and-dry on moving faces, please make sure you clean them thoroughly.
Click to expand...

Hi Mako, I did wipe off the shaft after use, as one does.
As for not running the engine with it disconnected for any length of time, It's been off for about 120 miles now but inspired by your comment I reconnected it for my trip home from work. Result, all of the original symptoms returned and didn't fade when the engine warmed up. Halfway through my 50 odd mile trip home I unplugged it again and bliss she drove normally.
So I haven't fixed the problem by stripping and cleaning the the valve, I'm reasonably confident the valve is working but changing it for a known good one is the only real proof. I'm still suspicious of whatever gives the ECU its signal to "choke" the engine.
Surely running the engine without the IACV functioning won't harm the engine much as starting a good old fashioned carb engine without using the manual choke merely makes it a little trickier drive start or drive until she warms up a little. Reading Procomm's link below confirms this for me.
Or have I missed the point entirely, if I have then all advise welcome.
 
Its not quite as simple as a choke, it would be interesting to know if its open or closed when disconnected, I suspect it is closed and when you connect it you close the circuit, I have stripped and cleaned 4 myself and you still get issues with them, replace with a known good (preferably new) one and disconnect battery for half hour to reset ecu then drive for several miles so it can re learn (y)
 
You must log in or register to reply here.