hunting idle

[richrx]

hi

i think ive got another TPS related problem. About 2 months ago my series 5s idle went to S***, it would stall once the engine had heated up, i re-adjusted the TPS and got the idle to 800rpm, however sometimes when hot she would still idle about 1500rpm, untill either she corrected herself or you dragged the rpm down by selecting a gear at a stand still and partially engaging the clutch quickly and disengaging it before she stalled.

when she was driven she would drive fine untill the revs dripped to 2,000rpm when she would kangaroo, sometimes quite violently! and the revs would stay at 2,000rmp even without applying any gas! so somthing wasnt right.

I then took her a 1200 mile drive round Skye, and other than the problem above she preformed perfectly although the problem did worsen slightly. When i arrived home i left her for a day or two and when i started her she wasnt happy at all...

there was no warm up procedure to 3-4000rpm as usual, insted she hunts between 1300-1600rpm regardless of throttle position! if you try and drive her she keeps doing the same, full throttle clutch in or out she does the same...etc

I think it sounds like the TPS may have given up the ghost, does that sound right or should i be looking anywhere else?

thanks for your help again!!

Richard:Thumbs-up

[fil_auto]

checked that your leads 2 plugs are connected up nicely - in good order?

[Prof]

The hunting could be TPS adjustment, but sounds like you maybe have another issue in there as well.
 
Things to check:
 
1) Timing - get a timing gun on - on the leading plug - front rotor - with revs below 900 rpm - you should be on the first of the timing marks (Make sure you warm it up before hand)
2) Vac Leaks - hunting or dying idle when warm.
3) Throttle cable too tight
4) Sticking throttles - they should move freely
5) AFM - check the connector to the AFM is in properly - and tight.

[richrx]

yep got everything hooked up as its ment to be, nothings out of place, theres no misfire so the plugs and leads are fine.

The hunting could be TPS adjustment, but sounds like you maybe have another issue in there as well.
 
Things to check:
 
1) Timing - get a timing gun on - on the leading plug - front rotor - with revs below 900 rpm - you should be on the first of the timing marks (Make sure you warm it up before hand)
2) Vac Leaks - hunting or dying idle when warm.
3) Throttle cable too tight
4) Sticking throttles - they should move freely
5) AFM - check the connector to the AFM is in properly - and tight.

I\'ll be checking all the above over the weekend, by throttles you mean the butterflies in the throttle body?

oh on a couple of occasions when hitting positive boost, at 3.5k rpm its stuttered and splattered... could there be a problem with the secondary injectors? its not a hesitation, its like hitting the limiter.....

when i tested the resistance it showed over 6 ohms on full throttle on the TPS, thats why im thinking its failed also.


thanks

Richard

[Prof]

The secondaries stage around 3800 rpm - so if they were failing that might explain the stuttering at that rpm - but they won\'t be anything to do with your idle issue.
 
Your car is an S5, so you\'ve got the 6 pin plug for the TPS (narrow and full range).  From memory, both pots are 5K or there abouts (might be a bit more), if you chase the wires back there are three going into each of the TPS potentiometer.  2 of these will have the full resistance across them, and the other is the \'wiper\' contact which varies between the 2 fixed points.  The 2 fixed ends of each potentiometer are wired to ground and to the 5v reference from the ecu respectively - so with a multimeter on the 20V range - you\'ll see 5V on 2 of the 6 pins in the plug, and 0V on 2 of the others.  The narrow range TPS is the one nearest the front of the car - once the car is warm, measure the resistance between the variable wiper contact and the wire that connects to 0V - you\'re looking for around 1K resistance with the throttles at rest (with car fully warmed up).
 
I\'ve got my intercooler off at the moment - so I will take pictures of the unit and the plug tomorrow morning and post them up - showing which wires to test and so forth.
 
By the way - the TPS wires are not 3 in a line like you might think, Mazda have wired them in such a way as to be in diagonally opposite corners !

[Prof]

Pics as promised:
 
The first 2 shots show the Wide and Narrow TPS resistors - the one nearest the alternator is the narrow range one.  Black/Green/Orage is the wire colours for it.
 
The next 2 shots show the wiring at the connector - note how they are wired into the corners - not along the straight edge as you might expect.
 
Finally there is a shot from the top - you can see the 2 TPS resistors clearly, and also the adjuster bolt with spring for adjusting the TPS narrow range just under the Narrow TPS.  It\'s a pig to get to with a stock inter cooler on, but you can just about get a really long narrow screwdriver on it - but be careful you don\'t short out on the alternator positive.

[richrx]

thanks for that! i replaced the TPS with a used one i had lying about and hey presto it runs with no issues well apart from a high idle, although thats just an adjustment i hope !!

I think its been failing for a while and ive been having a few issues with low idles etc too. im much happier with it!

thanks again


Richard

[Prof]

Excellent news.
 
Yeh - idle rpm\'s should be just a matter of adjusting the small screw in the Bypass Air Control (BAC) valve.  You should switch off any electrical loads (A/C, Heater Blower, Defroster, Headlights) before trying to set the RPM\'s - as those things all trigger the BAC valve to let more air in to compensate - hence they will increase revs.  I think it\'s also an idea to have your steering straight - as power steering pump also causes BAC adjustment.
 
Some Jap cars didn\'t have the aduster in the BAC - for these you need to play with the idle adjuster on the throttle mechanism - not sure which screw that is, I\'d have to go look at the manual for it.
 
Again with RPM adjustment - you should do it when the engine\'s warm.  Also, once you\'ve got it below about 900 RPM, check your timing - if it\'s out, the revs may drop/increase as you get the timing on the mark, so you may have to adjust rpm again.
 
Finally, once you\'ve got the idle RPM sorted - go back and check TPS - it should still be ok, but I\'ve had to set it again after taking the car for a long drive after sorting idle issues out.