theDevilX

Apparently these problems never end! I appreciate that it may have been answered before, but I've not found any solution so far.

My FC (NA) was idling pretty well up until yesterday, a little rich and burbly, but not bad.
The only idle issue I had was that the fast idle cam was stuck and I had to keep the car alive with the gas pedal when cold.

Yesterday I took off the UIM & throttle body, removed the cam for the fast idle, cleaned it all up, set it and reinstalled it, while there I removed the two tertiary plates that are there to stop people using full throttle when the engine is cold, I left the shaft in, just slide out the plates.
While the access was good I removed the alternator to find a local scrapyard replacement.

I then reinstalled everything and since then I've had this extremely lumpy idle, if I rev it just slightly its so rich it pops and bangs from the exhaust, the engine is shaking the car, especially noticeable through the gear lever, the idle adjustment screw makes very little difference, as does the mixture screw.
I've triple checked all the vacuum pipes and even sprayed easy start around all of them to see if the engine picked up, no joy.

I'm honestly stumped, I've had the UIM off loads of times before with no issues, I even removed the air pump belt again in case that was causing it, no difference.

Does anyone have any ideas?

lduley

iTrader: (1)

stupid silly question, did you remember to plug in the TPS?

theDevilX

Yep, TPS plugged in, same for BAC valve and the sensor under the BAC. I've no idea what I might have changed that would cause these problems. This is definitely the most temperamental car i've worked on!

Could a bad ACV cause this kind of problem?

insightful

post a video and cross your fingers a nut didn't make it down the intake while you were working.

theDevilX

I will do in the morning.
Doubt a nut made it down there because they're all accounted for, That and the fact the engine hasn't self destructed.

WondrousBread

First, there is an adjustment procedure for the fast idle cam and thermowax in the Factory Service Manual, did you follow it? Or was it by eyeball.

Second, the throttle plates you removed are the ones connected to the little vacuum actuator, yes? Not the inner ones? The three on the engine side are required, it is the outer two closest to the passenger fender you can remove. Bear in mind that the shaft that they rotate on is also held into the TB by the plates. Without the plates, the shaft is free to fall out whenever. You can keep the little vacuum actuator installed to retain it though, and it will rotate as normal but without blades it won't make any difference.

Third, there is a Factory Service Manual adjustment procedure and specification to set the opening time for the secondary throttle blades (it is a clearance between the blades and the barrels of the TB that must be within a certain specification). If you rebuilt the TB and it's linkages, you probably have to adjust that.

theDevilX

Yes I followed the service manual procedure for setting the fast idle. When the engine is warmed up the cam is completely disengaged as it should be. (But my idle problem remains)

Yes I removed the correct plates, I left the shaft and actuator in place as I didn't have anything to seal it up with at hand.
I didn't rebuild the whole throttle body, just the stuck fast idle cam, I've not touched anything that would effect the normal throttle blades.

insightful

id still start by checking the health of the engine, half the engine could be working perfectly and the other half doing little to nothing.

the main problem is, these engines rarely pop and backfire unless unburnt fuel is making it to the exhaust, which means either half the ignition isn't working or half the engine isnt.

theDevilX

I think we're getting ahead of things here.

The engine was working perfectly, I took the intake manifold and alternator off, changed some belts refitted and its now it isn't.
It seems more likely it's something I've done then just the engine wearing out.
It behaved the exact same way when I tried disconnecting the vaccuum source to the ACV a while back, only its not that this time.

Since I've tried everything I can think of, I'll just have to strip the UIM off again and see if I can spot anything.

insightful

spending 5 minutes on a compression test

or

spending a day tearing apart the top end of the engine and creating possibly more potential issues



i'm not sure why everyone has to argue with me constantly about doing a simple test to rule out the main component. these engines can have issues for no apparent reason after running perfectly fine the day before. carbon locked seals, junk making it into the engine regardless how careful you are, other internal factors that cause detriments like improper lubrication/supplements, etc.

you also likely have a distributor versus a crank sensor and DIS being a eurospec car so i would also suggest taking a look at your cap, internals and ignition wiring routing. your ignition system is weaker and more prone to problems with the distributor.

theDevilX

The engine runs absolutely fine apart from at idle, its not down on power compared too how it was, literally the only time it runs any different from a couple of days ago is at idle. No starting issues, hot or cold. Just running rough at idle.

A compression test is a 5 minute job if you have the equipment. There's no where near to me that does rotary compression testing.

The dizzy cap and rotor arm and leads were all replaced as one of the first jobs when I bought the car about 2 months ago. (Done around 1,000 miles since)


I'm not trying to be confrontational about the compression test, but since the car runs A-OK apart from at idle, and I've had the UIM off, it seems far more likely that it's something I've caused rather than an actual engine internal problem.

Regarding the ACV, is it normal for the engine to completely die if I pull off the vacuum line to the top of it? Or does that indicate some internal leak in the valve? (Just to clarify when pulling the line off the ACV that means putting my finger over the hose I've pulled off to make sure I'm not introducing a leak at the other end of said pipe)

DankestKush

iTrader: (4)

just rent a piston compression tester and remove the schrader valve.

Rotary Alkymist

If you put the plates back in you will fix your idle issue.

psyaddict

maybe the engine bridgeported itself

theDevilX

In a way the idle does almost sound like that, but nowhere near as extreme.
Its running better now after more tweaking, but still not right.

There was a huge vacuum in the fuel tank when I removed the cap so I guess the breather is blocked, it ran immediately better after that, but it still a good way off.
I'm seriously leaning towards the ACV as I get lot of popping and juddering on the over run.

insightful

if you/someone else inadvertently used the secondary butterfly set screw to up the idle then the idle will get extremely choppy. some people mess with that screw because it is easy to get to where the actual primary butterfly set screw is inaccessible on the n/a throttle body while it is installed.

does your car also have a variable resistor?

other things like putting a walbro pump in will cause an excessively rich condition due to overpressurization.

NCross

iTrader: (18)

There is a lot to go wrong under the UIM if not reinstalled correctly. It is impossible for anyone here to diagnose this problem from afar. Only you can check your work.

The likelihood of something being adjusted wrong on the TB is high. Been there done that. The "TB Mod" isn't worth it. Personally if it were me... I would source out another decent condition TB with factory settings and start from there.

insightful

that's easier said than done, even half my throttle bodies from over 10 years ago i have on the shelf have been dicked with, 10 years later i'd say it's highly unlikely to even find ones that someone hasn't messed with at some point. irony being they almost never actually need to be adjusted aside from the TPS and repairing the thermowax.

theDevilX

The throttle body is standard apart from me removing the restriction plates that stop you from using full power from cold, I didn't fiddle with anything else. I guess a previous owner could have fiddled, but as its been running fine up until now probably not.

Sourcing anything non molested for these cars in the UK is near on impossible. There are only 63 left on the road!

(Yeah I do have the variable resistor, however adjusting it has only given a limited improvement.)

Thanks for all the suggestions. There's probably not a lot more to say until I remove it all again.

TonyD89

iTrader: (10)

Shipping something like a throttle body from the US to UK shouldn't be too bad. I'm sure you could find an unmolested one in the for sale here.

insightful

if ~$100 isn't bad, then yeah you'd be correct. shipping first class offers no guarantees or insurance, but the only affordable way to ship, but then the seller is holding the bag if anything happens. i've had a number of packages wind up lost through the years going overseas and USPS just shrugs if you don't at least ship priority or higher internationally.

the only thing that would cause a rough idle on the throttle body would be the TPS and/or secondary butterflies propped open too much. the secondaries are easy to rule out, back off the secondary stop screw until the idle drops until it stops going down and then turn it back in about 1/16 turn and lock the nut. the secondary butterflies ideally should be closed, the only purpose of the set screw is to prevent the plates from binding in the bore and causing the gas pedal to stick at idle. any air getting to the secondary ports causes the overlap in those ports to cause a lumpy idle to occur, add in the fact that there is no fuel being injected into those ports at idle and you see why that isn't ideal.

theDevilX

It's certainly something else for me to check out, I'm at work now until Tuesday so no time for the car until then. (12 hour shifts)

I'm almost certain its not anything on the throttle body, linkage wise etc. I've changed nothing apart from removing the fast idle cam, cleaning and refitting, and the two butterflies at the front.
I didn't touch a single thing on any other part of the throttle body. And given it ran perfectly well before I'd imagine the settings can't be too far out.

I'm at the point now where it makes sense just to remove the UIM, go over it and anything I might have dislodged with a fine tooth comb. I have another ACV from my other engine, so I may fit that to see if it makes any kind of difference.
I also have another throttle body, but since its off a car with twice the mileage and then sat unused for 20 years in someones garage, and all the parts that had coolant on are basically corroded paper thin, I doubt it will be any better.

Rotary Alkymist

Ok, so I read this whole thing again and there are a few things that you did incorrectly.

I'm running an s5 but the setup is basically the same.

If you change your zero throttle position then you will change the TPS setting. You cannot change one without changing the other.

Example:

Primary throttle clearance has tampered with. Let's say it's set too high.

What you'll notice is, when you set the TPS to proper setting you're idle will sound very smooth but it will be too high... let's say 1000rpm.

Then you'll think, well it's idling perfect now all I have to do is lower the idle and you do. Now your idle is lower but it's not smooth anymore... because the TPS is out of range.

You will be driving yourself crazy going back and forth between settings. In some cases you'll lose track and you'll tighten the TPS too much and you'll run out of adjustment.

It's important to have it set as Insightful explained and THEN set the TPS.

I hope this makes sense. Again I run s5 so I don't have the idle screw on top like you.

theDevilX

It does make sense, but I think I probably didn't explain what I did accurately in my earlier posts, I've not actually effected my resting throttle position (apart from when the engine is cold) this is what I did, in the order I did it.

- Engine was running well and idling perfectly... Apart from requiring throttle to keep it alive when warming up. I suspected most likely that the fast idle cam operated by the thermowax was sticking.
- I also noticed that the air pump belt was glazed, and a little loose (it was possible to turn the pump without the engine running, albeit with some friction). As it was old and stretched, I was unable to tighten it.

- I removed the UIM & throttle body

- At this point I replaced the alternator and airpump v-belts.

- Inspecting the fast idle mechanism, it was stuck in the 'off position'. i.e. the cam plate was not touching and it wasn't effecting the idle in the slightest.
- To gain access to the mechanism I first had to remove the dashpot. I didn't adjust this, simply undid the scews holding it onto the throttle body
- Next I removed the fast idle cam and spring, cleaned up the shaft and reinstalled, it was now moving freely.
- Now I set the fast idle as per the workshop manual using the marks on the cam plate and the spring loaded screw that pushes onto the thermowax.
- Reinstalled the dashpot

Now to remove potential vacuum leaks and because I won't ever go full throttle when warming up I decided to remove the secondary butterflies that are only used on an NA to prevent full throttle when the engine is cold.
- I unscrewed and slid out the 2 butterfly plates, but left the shaft in place with the vacuum actuator still attached as I had no way to fill the hole that it would leave.
- I capped off the port on the UIM that supplied vacuum to the secondary butterfly actuators.
- Finally I reinstalled the UIM, reconnected all sensors / hoses / vacuum lines + the throttle cable.


Now when I first started the engine, I got all the symptons previously described, it. But it would idle cold, when previously it didn't, so to an extent that was better.
After letting the engine warm up fully I made sure that the fast idle cam was fully disengaging (it was), and then checked the TPS calibration. (Still spot on)

Other things I've observed when driving.
- Car sometimes has a hesitation around 4rpm that it didn't have before
- Engine runs smoothly in normal driving, just the idle seems affected.
- Under decelleration, car is now a lot smoother whereas previously it used to be a bit rough (which is leading me to suspect ACV)

When I'm next off work, I'll go through the TB and using the workshop manual, double check every clearance, setting and anything else that's in there.

Rotary Alkymist

I know when you search this topic on this forum you have reputable members explaining that the power increase is a placebo and it only leads to idle issues. Unfortunately I have no first hand experience to share.

Are you checking the TPS with the diode method? Mazda's diode method is supreme imo. I set my TPS to 1v and it was very close to perfect but it wasn't perfect because both lights were on when I tested via diode method. I forget what my voltage is on my TPS is but do remember that it isn't sitting at 1.00v.

If nothing else has changed accept the removal of the plates then I would suspect, logically, that the problem has cropped up because of the mod. If all else fails I would reinstall the plates and see if it fixes the issue.
Keep us updated!