Punto 75SX Eratic Tickover

I've had a number of electrical problems with this car but it's running quite well at the moment.
EXCEPT: Every now and then it starts revving up on its own accord. The car
starts and run ok but after driving for a while it takes it upon itself to vary between 1000 and 2500 revs. This looks and sound bad if you're stopped at traffic lights and even more so if you're waiting for someone walking across a zebra crossing. There is also an increase in fuel consumption.
Has anyone got any suggestions?
Cheers
Rick
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What year is your PuntoSX and is a Fuel Injected or a carb fuel system?
Nick /////

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Hi Nick
It's a 96 N reg 1.2 8-valve multi-point petrol injection.
Rick

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You sure it is a multi-point and not an SPI (Single Point Injection)?
Also change your Email address to something like snipped-for-privacy@localhost.invalid otherwise if not already too late the SPAM robots will grab your email address and SPAM you to death!
Nick /////

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Hi Nick
Yes, it's states Multi-Point Injection on black plastic oil filter housing and also MPI on the ECU. The 'log' book says 1242 cc.
Rick

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Ok.
Without digging deeper I'm now assuming that the 1.2MPI is essentially the same as the Magnetti Mirelleli MPI unit fitted to the Tempra 1.8ie.
Follow this:
Locate the manifold inlet tubes at the cylinder head itself. Follow them back and possibly upwards. They will probably all meet/interface with a large chamber/body that joins them together. This is the plenum chamber. At one end of this is the throttle body. After the throttle body is a large tube assembly that leads to the air filter and beyond. Around either side of the throttle body there may be two hoses (obe either side) that lead off to a valve, called the air bypass valve. This may be located at the end of the cylinder head above the gearbox and between the battery box.
The purpose of this valve is to act as a variable bypass around the throttle plate thus adjusting the engine idle revs. They are know to stick with age.
Here is the contents of a post I have made on this in the past. (22 April 2007)
1) Check for leaks/cracks etc in all air hoses attached to the inlet manifold. This include the brake vacuum hose. Also operate the brake pedal and listen for engine speed or note changes.
2) Sticking idle control solenoid - this could be either a mechanical operation on the throttle butterfly or an air bypass valve. If you have an air bypass solenoid then one should service this as sticking is a known problem. Easy to do. Just remove the valve and inspect inside. Gently remove any deposits. Flush / fill with WD-40 and agitate. If it is really dirty then wash out with white spirit, dry and give a very good soak with WD-40. Another trick is to allow the engine management system to modulate the valve when you have WD-40 in it. Easy to do by only making the electrical connection, fill with WD-40 and hand/finger seal the hose connection points and then get somebody to turn the ignition on (DO NOT START). The ECU will open and close the valve a couple of times. Repeat ignition on/off cycle a few times.
The valve is officially called VAE Valve.
3) Incorrect static air bypass setting. Tempra Magnetti Marelli fuel injection systems had this identified by a grub screw and locking nut located on the throttle body. This sets a minimum air bypass and thus idle speed so that the air bypass valve has a nominal point about which to operate. To set this up one has to disconnect the electrical connection to the air bypass valve. The car should not stall be yours may. If this happens then reconnect the valve. Adjust the grub screw out. Initially nothing may happen as the bypass valve will automatically compensate for your adjustment. Get the revs to about 1000rpm. Now you can disconnect the valve connector and proceed to adjust the grub screw till the revs are about 650 to 700rpm. Now connect the valve connector again and the revs will briefly rise to about 1200 rpm or so and then drop back again to about 850 rpm.
Lastly blip the throttle and check that the car does not stall or idle too low. Test drive as well. You may find that you have to have a couple of cycles in setting the bypass grub screw. Setting too low revs will cause stalling etc. and too high will mean too fast and idle.
4) If all of 3) still does not work to your satisfaction then there was a Fiat service bulletin that modified the original set-up as in 3) to actually set the grub screw get engine revs of 900rpm (or as low a you can get to 850rpm) so that when the VAE valve electrical connection is removed/connected there is NO variation in rpm. I never had to do this as I found that the method and settings in 3) was perfectly OK for my Tempra. You may find that you need to go with this 4) method.
Lastly if the Marea uses a mechanical solenoid directly operating on the throttle body butterfly (Most Fiat single point injection systems like in the Tipo use this method) then just like the air bypass grub screw in 3 & 4, there will be a similar grub screw to set the base throttle opening from which the solenoid lifts the engine revs.
I leave the rest for you to sort out :-)
Nick /////
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Hi Nick
Many thanks for the information.
My 'tame' mechanic has now helped me have a go at this but we couldn't remove the control valve as one of the screw heads became mashed. So we tightened the unit up again and gave all connections lashings of WD40 and it's now running better, not perfect, but loads better (good enough to sell). This seems to confirm it may be the idle control valve so I am now going to replace it. I've found them on eBay for 20-25 so it's worth a try. Although it seems tricky working out which one to get. Have tried reading the part number on the side of the existing valve but it doesn't match what the 2 companies state on eBay.
I'll update you when I sort it out.
Thanks again.
Rick

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Yikes, don't use WD-40 on electrical connections. Use DeoxIT (www.deoxit.com). For mechanical us WD-40, for electrical use DeoxIT Mike
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Yikes, don't use WD-40 on electrical connections. Use DeoxIT (www.deoxit.com). For mechanical us WD-40, for electrical use DeoxIT Mike
Easy to do by

I didn't say, although I can see I badly worded the post, to apply WD40 to the electrical connections :-)
Having said that I have for many years used WD40 or other very light oil on NON-SWITCHing contacts, especially engine bay connectors with no problems at all. If used correctly and sensibly it is not an issue.
dexoit, switch clean/lube are excellent products however. They clean and lubricate but are however not very good at providing long term moisture and damp protection. For non switching contacts like connectors there is direct metal to metal contact of quite high surface pressures. These displace and penetrate any suitable light oil with easy. The contact area is then surrounded by a moisture repellent film that ensure the metal to metal contacts remain moisture and corrosion free.
You can get special custom made lubes that do this but they are not readily available to most to WD40 is a good substitute if used correctly and moderately.
The following are just some of the approved uses for WD40 (www.wd40.co.uk)
Cleans gunk from electrical contacts Drives moisture from electrical wiring in cars Protects electrical connections in car/truck engines Lubricates and improves electrical contacts on model train tracks Cleans electrical contacts on slot racing cars
Nick /////
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Yikes, never use WD-40 on electrical contacts. May work for a short time, but will gum up and attack the plastics and parts after a while. The only thing to use on electrical contacts and connections is Deoxit, www.deoxit.com, actually chemically improves connections after it cleans it. Stuff is amazing and is safe on just about every material. Try it, you will not use anything else after you try. Mike
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Nearly 20 years use of WD40 on ONE car, from new, on electrical connectors, including wires, contacts, casing & rubber seals has never produced any problems. In fact totally beneficial. Plenty of other cars of varying ages of continual WD40 use all perfectly OK as well.
Nick /////
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To each his own. I use products that are specifically designed and tested on their particular use. I use WD-40 and other mechanical lubricants for "mechanicall applications" and DeoxIT products on "electrical applications". Mike
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