3.5l v8 efi 1983 kit car idle problems and questions

Good evening everyone

Just signed up here as i have a kit car with the rover v8 fitted.

the car is an evolution roadster built in 2002 with all the bits taken from a rover sd1 on a 83 plate (A)

I've had the car a few weeks now and spent the weekend having a proper look over it, its got some issues and i thought this would be the best place to ask for some help.

today i replaced all 8 spark plugs and im awating a distrubutor cap and leads and a coil, it had a misfire but didnt when i bought it so changed out the plugs and its all good now, however the problem is on tickover once its hot, once i rev the engine as it comes back down to idle it doesn't drop fast like it should when its cold and stick to idle, it stays about idle about 1500rpm.

today i removed the plenum chamber, cleaned it, re sealed it, re fitted it, had all the breathers off and cleaned and checked those, unplugged the 9th injector on the plenum and blanked off the fuel pipe also. Also removed the extra air valve, cleaned it and refitted.

it has a FSE power boost valve fitted, i removed that opened it up cleaned it out didnt find anything of issue there. After much tinkering and messing around the TPS on the plenum butterfly was clicking when i moved the wires around it and was making the car run differently, i removed it to inspect it and the green wire 1 of 3 that goes into the tps just came away, so i opened it up and its pretty much knackered, i ran the car with out the TPS and unplugging the breather pipe which comes from the O/S rocker cover and the car starts up perfectly, drives nice, and when i rev it drops back to idle nice and quick like it should. Im a mechanic by trade and i know how the TPS works and with ecu's etc etc, its just confusing me because all day messing around with it, with the breather attached and the TPS on its not sat at idle, when they are removed its running absolutely fine and this doesnt make any sense to me haha.

so can i just stick a filter on the end of the butterfly breather to atmosphere, and am i going to cause any damage to the engine running with out the TPS? It's totally unplugged and not on the engine now as its broken. Out driving it pulls hard in every gear with no problem, no lack of power at any point in the rev range.

any help on the matter would be appreciated.

i did read they don't sell those TPS sensors any more so a modified one from another engine can be used.

The TPS can be found, but high priced.
There are also kits that allow you to use other TPS, but again not cheap.
Is it possible your TPS was sticking & not allowing the butterfly to close? - bearing in mind the flapper system needs a slight airgap set with a 0.05mm/0.002in feeler gauge at the bottom of the butterfly.
The flashback arrester on top of the rocker cover can block, as can the breather passageway in the plenum. My RRC was completely blocked & needed a drill bit finger operated to break up the solidified crud. Whilst not being able to breathe didn't cause any running issue it did cause oil leaks from all sorts of interesting places! The metal pipe that the breather pipe pushes onto on the plenum is an interference fit & can be removed to help access.
ETA As your donor was an SD1 there's a lot of stuff on this Rover SD1 link that might be of interest. Some of the workrounds aren't possible as the alternative parts are NLA.
http://www.vintagemodelairplane.com/pages/Rover_Technical/ThrotPot01.html

Ok so the TPS isn’t motor fed, it’s just for a reading back to ecu from what I remember. It doesn’t have any control on the butterfly what so ever. I had the plenum off and cleaned it the butterfly looks fine it wasn’t that dirty.

I’ve had all the breathers off and all clear, no cracks. Even in the metal one that runs underneath were all fine.

Baffled how it’s running so good with out the TPS, just worried it might be running lean on full throttle with out the ecu knowing to throw the extra fuel in but when I’m out driving the Rev range and power band is spot on no flat spots or anything. I’ll do some miles and check the stare of the plugs, should give me a better idea about the mixture.

Joker1988 said:

Ok so the TPS isn’t motor fed, it’s just for a reading back to ecu from what I remember.

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Correct.

Joker1988 said:

It doesn’t have any control on the butterfly what so ever.

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But it is operated by the butterfly shaft, so if it's sticking could interfere with the butterfly closure.

Joker1988 said:

I had the plenum off and cleaned it the butterfly looks fine it wasn’t that dirty.

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It was the internal passage in the plenum that was solid on mine. Turns 90deg from the metal pipe to face the offside of the car, then 90deg to face the rear of the car a bit further along to enter the plenum through a hole you can see on its inside by the butterfly. Needed to pull the metal pipe to be able to use the drill bit from the nearside of the plenum then flushed through with thinners in a squirty bottle. The butterfly is usually OK, dirt deposits build up where it closes, effectively blocking the required air gap when closed.

Joker1988 said:

I’ve had all the breathers off and all clear, no cracks. Even in the metal one that runs underneath were all fine.
Baffled how it’s running so good with out the TPS, just worried it might be running lean on full throttle with out the ecu knowing to throw the extra fuel in but when I’m out driving the Rev range and power band is spot on no flat spots or anything. I’ll do some miles and check the stare of the plugs, should give me a better idea about the mixture.

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As you'll lack the pulse input for a sudden 'foot down' I'd expect your acceleration to be slower.