Author Topic: Fluctuating Idle Fix  (Read 3549 times)

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Fluctuating Idle Fix
« on: February 18, 2011, 05:16:52 PM »

The F300 Daihatsu Feroza had an unstable idle when purchased - it would change RPM about every two seconds by about 150/200 RPM. The previous owners advice was \"they all do it\". Don\'t know if its true but.......

Turned out to be the throttle idle switch was not closing leading to the engine running on the exhaust oxygen sensor - causing the hunting.

Tried to adjust the standard switch, but its an incredibly poor ( read sub-standard ) design - very thin switch contacts that age and bend out of adjustment. Be carefull if you try this - if you get the contacts vs position wrong the engine cuts out ( thinks its in over-run ) and this is \"distressing\" when driving......... I gave up trying to fix the old one and I have reasonable engineering facilities - so its not recomended for the inexperienced.

Much to my pleasure a standard BOSCH unit bolts directly on, and its a much better unit as it contains a micro switch thats much more accurate and reliable, will last forever.

The oxygen sensor also was at near the end of its life - once again replaced with a new standard BOSCH unit. The net effect was a noticible improvement in economy, and of course a stable idle. Runs a Lambda of 1 virtually all the time ( so the EFI systms not bad for its day )

Remember an oxygen sensor \"breathes\" via the connection wire sheath so don\'t crimp the sheath or use silicone etc else it won\'t work properly. Was able to reuse the old connector as the standard universal fit one was different.

The Bosch oxygen sensor for a F300/310 ( HD-E ) is a 0 258 002 031. Because the old one\'s in the exhaust they can be hard to get out, so use a tight fitting ring spanner and watch your knuckles. The new sensor has anti-sieze pre applied so no extra is needed.

The Throttle Position Sensor ( TPS ) was made in many variants, for different countries so a number is useless for most people. However all the variants look the same, are mechanically and electrically similar to the original and plug straight in.
They were fitted to older cars with BOSCH L or LE EFI systems so don\'t waste you time on new models

Likely candidates are Volvo\'s Alfa\'s BMW\'s, Fords, some GM etc. just check the shaft bush fits on.

It has two switches inside, one for idle and the other for full load. When you replace the TPS it is necessary to ensure the idle switch just closes when the throttle is fully closed. The TPS has slotted holes to allow for this adjustment. A multimeter is required to check the switch closes - take the time to get it right.





Testing procedure is on page EF-61 of the F300 manuals and the only tools required are a screwdriver and multimeter. The TPS wiring loom and plug have a small metal retainer which must be gently levered off before the plug comes away - don\'t force it.

I think I have this problem, what are the part numbers?

TPS has 2 BOSCH part numbers on it.

B 280 120 507
D 280 120 316 ( 6 might be an 8 - it difficult to read.... )

Before you dive in you can do a simple test to prove where the problem is.

Test A:

Use a multimeter to check for a closed circuit between the centre and bottom terminals of the TPS when the throttle is closed. Any rotation of the throttle should break this circuit.


Test B:

Warm up the beast and turn off.
Disconect the TPS plug.
Start the beast and let idle.
Connect the centre and bottom terminals of the TPS plug with a piece of wire. ( That simulates the TPS idle switch closing )
Wait a few seconds.

If the idle instability goes away - then there\'s you problem

Remember a whole range of cars were fitted with useable variants of the TPS so a second hand unit will save $$$ - just make sure the small plastic shaft adapter that goes between the Diahatsu throttle shaft and the BOSCH TPS is the right shape.

When replacing ANY TPS its necessary to set it up so that it closes at the right time. The mounting lugs are slotted to allow adjustment. The BOSCH unit produces an audible click when it closes so just make sure that when the throttle is fully closed the TPS has just clicked. Try this a few times to get it right then tighten the mounting bolts.


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Re: Fluctuating Idle Fix
« Reply #1 on: August 17, 2015, 10:54:07 PM »
so i tried this and it works.

Quite a few old school bmws from the 80s have the correct sensor.

According to a BMW wrecker i contacted, they can be found on the M20 motor or BMW E30 - 270 E34 and  E28 underneath the throttle body.

They are quite often filled with oil, mine was, however it works

Offline eintier

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Re: Fluctuating Idle Fix
« Reply #2 on: February 08, 2016, 02:21:40 PM »
I'm having some idle issues.   Where do I find the TPS?