MK1 MX5 1.8 - Is my Throttle Position Sensor Bad?

Technical Area Engine, Transmission, Exhaust etc
2

Hi, on start up my engine idles fine, then once it is warm, the idle becomes lower and when you drive it and pull up at a junction it almost stalls. When i put my foot down the power feels sticky and takes a while to creep up the revs, once at 5k revs it runs smoother but still doesn’t feel right. Here is a short video on the idling 

https://www.youtube.com/watch?v=nLuaoCmdL8Y&feature=youtu.be

Any information would be welcomed, I’ve also questioned a block cat and maybe the temp sensor is out. Also what is a Lambar sensor?

 

3

Sounds like she needs a good service and engine flush first?,have you tried lubricating the throttle mech, and running a flash code?.

M-m

4

hello, the car had a service before i bought it, i checked today aswell and it had a brand new air filter (i know it doesn’t mean everything was done) but it gives me some hope.

Whats the best way to flush and engine, ive been on youtube and some of them seem alright but not harsh enough… also iv’e heard that its a terrible thing to do to an old car!

I took the throttle sensor off today and drove without it on, the car ran smoother but still has no power where it should!

5

It sure is! I tried this on my 100K miler MK1 with disastrous results!  I used plenty of hot water and fairy liquid.  Initially It looked good with loads of creamy gunge coming out of the sump, then the engine rattled nicely as everything got cleaned and loosened up; but then the engine just stopped and wouldn’t start again.  Don’t think I’ll be doing that again in a hurry

 

6

To be honest, I’ve never heard of someone put hot water and fairy liquid in there engine, as far as “strange” goes is 2ltr of fresh oil and 2ltr petrol.

I know you can buy a bottle of flush fluid, contains chemicals to dissolve minor deposits, how ever on an old car the deposits are much larger, so instead of disolving it just break down, eventually the deposits get into places where theyre not meant to be and can break the engine. However, MX5 MK1 engines are beyond tough aparently and can take a beating, so im just wondering what the best way to do a flush on my mk1 mx5 with 115k miles.

7

I assume you are not taking part of Wayne’s advice to run a diagnostic, any reason for that.

8

 

Please confirm you are actually just having a wind up?

Apart from seeing a well known Celtic winger many years back filling up the OIL orifice in his new complimentary Merc with washer fluid, I have to say this eclipses even that wanton act of car murder.      

 

 

 

9

This may have been posted in jest, but please, please, please do not do this.

 

 

10

FAIRY LIQUID…well, that’s where you went wrong, you should have used valve grinding paste and sulphuric acid!

Joke or not i can not believe you posted THAT.

11

Soo… How do I properly flush my engine without damaging it. Or is it necessary to do?

12

It’s one of those debated subjects that rears it’s head now and then.

To be frank, I have never flushed with any chemical additives in 40 years, and that is having owned everything from a Mini Clubman to an Opel Monza Turbo, a Vulcan milled 2.8i,…and a Yugo! (don’t ask)

What I don’t like about the idea is that I don’t think you can bet 100% that all the chemicals are drained out the (narrow) oilways before refill.

Furthermore, it carries the risk of dislodging hardened and minute particulates in the oil system that before were not doing a lot of harm. 

 Long gone are the days of de-coking, mineral oils etc where these sorts of products (like Redex) slid off the shelves.

The best “flush” in my opinion is regular oil changes with a “by the book” lubricant. Modern oils do superb job of cleaning as you go. I’ve used Castrol GTX for decades in everything (NOT Magnitec) and never had an issue with any cars, many of which sailed past 100,000 miles and beyond.

In a Mk1 especially I’d recommend a full filter/ oil change every 6 months or 4k miles whichever happens first. Some will say that’s overkill, perhaps so. I would counter it’s peace of mind and cheaper than a new engine.

Sometimes, though not always, 1st start HLA clacking can herald tired oil…but it should go quiet in under a minute, nor does it suggest some mechanical mishap on the horizon as the HLA buckets are simply pressuring/filling up…unless you have one of the later cars with solid lifters.

Note with these engines around a litre burned off per 1000 miles is “acceptable” anyway so it pays to check levels every 500 miles or so and there must be plenty old 1840cc cars zipping around burning off a bit more especially if they are revved “properly”

As for the “service” my jury is out on that one. It sounds a bit off colour and “woofly” From the video it seems to idle OK, but I’d go through everything EG have the plugs out. Simple things like new leads & plugs on these engines can work miracles. Have the timing checked. Maybe someone tried the 14 degree tweak and it’s not worked. In short, get the thing as far as possible back to basics first. Depending on the year of your car, you can take the CAT out. I think it’s '94 or prior…I think.

There’s a lot of what looks like post-radiator burst surface rust going on…so perhaps a double check of all electrical connections is advisable.

( It’s Lambda Sensor btw)

13

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Thanks scottishfiver, very informational. I think ill go with checking everything to bare minimum first. If everything fails, ill try a flush. The main thing i wan’t sorted is the exhaust, if it still runs like it has 3 legged horses, i’ll change all sparks and leads then the sensors and upgrade the hoses. if that still doesnt work then the old timing can be checked. Also when i bought this apparently it had a new timing belt? Any way after that ill do a flush then after that if it doesn’t work it will be sold!!!

15

 

You mentioned exhaust.  Have you checked it is not blocked? 

It does happen, I once had to punch out a baffle on a Ford exhaust to make it a straight through!

16

Hi, im pretty sure the cat is blocked. The tail pipe had fell of through rust and the whole exhaust looks rusty too. So it could all be down to this, just trying to figure out for sure whats up with it!

17

You’ve mentioned “it’s just had a new timing belt” thats the first place i’d look.

18

And me, check the valve timing.

19

Engine oil, flush and filter are a red herring, and won’t make the slightest difference to the symptoms you’ve described.  Back to basics on the ignition, then exhaust, then sensors.  Good luck - and let us know when you’ve cured it!

20

George,

I am certain beyond any doubt spending cash on a flush & subsequent oil/filter changes will be throwing money to eradicate a completely different issue.

That cash will pay for new plugs & leads if required. Up to you though.