I have the wrong throttle body and/or intake manifold

[IamStandingBehindYou]

I've been hunting an issue with a low surging idle on my 325i E30, after a smoke test today it's been identified as a problem with a non-matching throttle body and intake manifold.

The smoke was coming out from the bottom of the throttle body where it joins to the intake manifold.

I'll be able to take further images once I get the car tomorrow, I happen to have this image on my phone as a reference as the car has the wrong rubber intake elbow and I was planning on buying the correct one. But now I'm wondering if it has the wrong intake elbow and throttle body?

My engine numbers are:

Top number: 256E2
Bottom number: 22364371
Head: 885




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[Cloggy Saint]

You've certainly got the wrong ICV for that intake elbow, or vice versa.

[Brianmoooore]

256E2 is a 2.5 engine, and that looks like a B25 inlet manifold, but as Cloggy Saint says, there's definitely been some bodgery going on, and it's rarely confined to just one place. Undo the four bolts that hold the TB onto the manifold, and let's have a look at what's going on.

[IamStandingBehindYou]

256E2 is a 2.5 engine, and that looks like a B25 inlet manifold, but as Cloggy Saint says, there's definitely been some bodgery going on, and it's rarely confined to just one place. Undo the four bolts that hold the TB onto the manifold, and let's have a look at what's going on.

I'll pull it off and post pics of both the TB and the manifold as soon as I get it back tomorrow. I've been researching TBs and I can't find any conclusive information about different ones being used on different 325i model years, but I assume there must be a difference if the rubber intake boot is different on some models.

[Brianmoooore]

Only production change made to the 2.5 TB was the deletion of the second port to the servo vacuum non return valve on late models.
Idle control valves come in straight or angled versions, and with that inlet hose, you need a straight one.

[IamStandingBehindYou]

Only production change made to the 2.5 TB was the deletion of the second port to the servo vacuum non return valve on late models.
Idle control valves come in straight or angled versions, and with that inlet hose, you need a straight one.

This might be a stupid question but do the ICVs all use the same plugs? Would a straight ICV just plug right in and work?

[IamStandingBehindYou]

Right, I got the car back from the mechanic this morning, took it home and pulled off the throttle body for a good look. Then I spent 10 minutes with my head in my hands trying to avoid the temptation to head for the whiskey shelf.

The previous owner has, for reasons that escape me, installed a throttle body from a BMW 528e. The bolt pattern is the same but the bore is far narrower, and the bottom part of the throttle body sits so high actually leaves a gap of a few mm - meaning the intake manifold can suck in outside air from behind the throttle switch.

I've attached photos below. The bottom image shows the gap, as you can see it's the correct gasket, and the gasket perfectly matches the face of the intake manifold - so you can clearly see the overlap.

Now I just need to find a good throttle body - is there any benefit to the "big bore" TBs I'm seeing online?

[aimlessrock]

bodgery is a sod to trace, but it looks like your making some headway. As opposed to a BTB I would be looking to get your car back to stock- I suspect you will likely find more bodgery as you dig.

Put an advert in the wanted section for a B25 TB and also look to also order a new set of gaskets and rubber blanking section from the stealers so you can give it a refurb before fitting.

Have you pulled the injectors yet?..would be worth checking these whilst your at it.

[Brianmoooore]

Mmmm! As Aimlessrock says, this won't be the last discovery. Looking forward to pics. of the electrics!
Wonder what the POs thinking was? It's from a 2.8, so must be better??

Good call about the injectors - the colour of the connector should be enough to identify if they are the correct ones.
There's two ways to solve the ICV problem - change the hose or the ICV, so it may be as well to check if the hose is due for replacement first.

[IamStandingBehindYou]

Okay I've just ordered a replacement throttle body and expedited the shipping, I'll now order a new gasket and a set of reconditioned and flow matched injectors. Are there any places you recommend getting injectors from?

[IamStandingBehindYou]

Mmmm! As Aimlessrock says, this won't be the last discovery. Looking forward to pics. of the electrics!
Wonder what the POs thinking was? It's from a 2.8, so must be better??

Good call about the injectors - the colour of the connector should be enough to identify if they are the correct ones.
There's two ways to solve the ICV problem - change the hose or the ICV, so it may be as well to check if the hose is due for replacement first.

I'll definitely swap out the hose too - might as well given how cheap they are, is there any difference in the ICVs? Or can I just use either?

[Cloggy Saint]

Internally the icv's are the same, it's just the shape that differs, L shape or T.

[IamStandingBehindYou]

bodgery is a sod to trace, but it looks like your making some headway. As opposed to a BTB I would be looking to get your car back to stock- I suspect you will likely find more bodgery as you dig.

Put an advert in the wanted section for a B25 TB and also look to also order a new set of gaskets and rubber blanking section from the stealers so you can give it a refurb before fitting.

Have you pulled the injectors yet?..would be worth checking these whilst your at it.

I hate to ask a stupid question but what is a rubber blanking section?

[IamStandingBehindYou]

Internally the icv's are the same, it's just the shape that differs, L shape or T.

Okay great thanks, I know the ICV I have is working so I'll swap out the intake elbow.

[aimlessrock]

bodgery is a sod to trace, but it looks like your making some headway. As opposed to a BTB I would be looking to get your car back to stock- I suspect you will likely find more bodgery as you dig.

Put an advert in the wanted section for a B25 TB and also look to also order a new set of gaskets and rubber blanking section from the stealers so you can give it a refurb before fitting.

Have you pulled the injectors yet?..would be worth checking these whilst your at it.

I hate to ask a stupid question but what is a rubber blanking section?

see the first picture of your 528 TB, note the port that has been blanked off with what looks like some kind of plastic screw bodge..(the one on the right of the photo) well the proper e30 part is a rubber blanking plug. I mentioned it as they perish and whilst your overhauling the TB you may as well replace it.. HTH

[aimlessrock]

Okay I've just ordered a replacement throttle body and expedited the shipping, I'll now order a new gasket and a set of reconditioned and flow matched injectors. Are there any places you recommend getting injectors from?

put an advert in the wanted section, make sure you state 325i (B25) as the B20 injectors are similar but have a different flow rate. Once you have a set send them to injector tune to overhaul and balance (check out the traders section- last set of mine he did he charged about £10.00 per injector..worth every penny).

[IamStandingBehindYou]

Right! I have the reconditioned throttle body fitted, there are also new (correctly gapped spark plugs), new fuel injectors (reconditioned and flow matched), and all the vacuum lines are sealed up tight.

The surging idle seems to be fixed, but it's still idling below 500 rpm, and the idle seems unsteady. Pumping the brake pedal temporarily fixes the problem, and the idle shifts up to a steady 750 rpm for a few moments until I stop pumping.

My plan going forward is another smoke test to see if anything was missed, I'm suspecting that either the brake master cylinder or idle control module might be toast. I just can't find much information about a low idle, most people seem to have problems with a high idle.

Is there anything you'd all recommend as far as troubleshooting is concerned?

[BenHar]

Sounds like an air leak though the brake servo.

Ben

[Brianmoooore]

As above. Pull the hose off of the servo or off of the one way valve, plug the end of it, and see if this sorts the problem.
If you drive the car like this, the brakes will work, but will need a LOT of pedal pressure.

[IamStandingBehindYou]

Okay thanks, I'll do this and report back with results.

[IamStandingBehindYou]

Just checking back in, I pulled off the 3 hoses that lead to the brake booster and sealed the intake side holes. I think there was a slight improvement initially but it went back to a sub-500 idle within a couple of minutes, taking off the oil filler cap caused a very slight difference in idle too, a barely perceptible drop. I did the recommended brake servo tests and it passed them both.

At this point I'm sure it's a vacuum leak from somewhere, but I just can't nail down where. I'm going to get a second smoke test done in the coming week to see if that will expose it. During the last smoke test we stopped looking as soon as smoke came out of the throttle body area but it seems that there is another leak further up the food chain.

I've also ordered a new intake boot and a new rocker cover gasket, so I'll swap them out when they arrive.

[BenHar]

Get a can of lighter gas and spray it round the intake with the engine running. The revs will rise if you spray near a leak.

Ben

[aimlessrock]

sounds like your making good progress Ian,..seek and you will find it. I was dogged with an air leak and ended up testing all the rubber hoses and found a couple of them had crack on the bends that were not detectable until removed and pressure tested (hand held tester i got from ebay).

[IamStandingBehindYou]

Okay second smoke test was done today and the problem is still the throttle body, but now it's a new part of it. The small press-in metal fittings on the right side to be exact.

The upper press-in fitting won't fit all the way into the TB, but I thought I had it jammed in the nice and tight. Apparently smoke came pouring out of it during the test so it's a far bigger problem than I thought.

The issue that I have now is that the press in fitting simply won't go in any deeper - I've tried hitting it with a BFH and no luck. I tried the press-in metal fittings from the previous TB and they don't fit at all because they aren't tapered.

Do I need to order a special part for this? Or should I take to the fitting with a file and round it off until it fits, then install it with ample gasket sealer?

Images below:

First pic is the throttle body with the upper fitting sticking out. That's as far in as it'll go even after being worked over with the BFH.

Second pic is the fitting showing the tapered end.

Third pic is the fitting from the other throttle body. It's not tapered and doesn't fit more than a couple of mm inside.

Fourth pic is both fittings together to compare.

[Cloggy Saint]

I would do away with the extra vacuum hose to the brake servo. Permanently block the upper hole on the TB with quicksteel or something similar, replace your double valve with a single one and get an intake elbow without the extra outlet.

[IamStandingBehindYou]

I would do away with the extra vacuum hose to the brake servo. Permanently block the upper hole on the TB with quicksteel or something similar, replace your double valve with a single one and get an intake elbow without the extra outlet.

Just saw your comment today after I'd already modified it to fit. I'd like to go down this route in the future though and simplify it all.

I used a fine-tooth file to take a tiny amount off the male side of the press-in fitting, I did it evenly all the way around until it fit flush with no wiggle room. I then used blue thread locker to seal it and lock it in place with a couple of solid hammer whacks. It's in very tight now with no leaks.

I refitted it all to the engine with a new TB gasket, double checked everything, then fired it up.

Same problem, low idle around 500 rpm.

I think there might have been a very slight improvement, but it could just be in my head. I uploaded a 30 second clip of the engine idling here - https://clyp.it/etkzqtjj with the iPhone mic just next to the oil fill cap. I'm not sure if that's helpful but I thought it's worth a shot.

Next plan of action is to take it for a 3rd smoke test and see what happens, if it's sealed up tight and there are no leaks then it must be something else - and I'll start down another line of investigation.

If it's not a vacuum leak does anyone have any suggestions about what I should check? I'm going to bleed the coolant again tomorrow when I find a hill to park it on, I'll also check the ICV and ICS for the umpteenth time.

Could this be anything to do with the rotor/leads/coil or fuel pressure regulator / fuel pump?

Thanks again for any help in advance!

[IamStandingBehindYou]

Back with another update:

After the 3rd smoke test the engine is now certified leak free, however the idle issues continue unabated. The mechanic that it's with now is an older guy who worked on these cars when they were new, and he seems to know his stuff.

He's getting an electrical specialist in to look at the AFM and make due it hasn't been messed with by the previous owner, he says that's his best guess at this point.

The engine still doesn't react at all when you take off the oil fill cap when the engine is running, in my experience these engines tend to idle low and run rough with the oil cap off - this is why I've been so sure there must be a vacuum leak.

I'll update when I know more.

[pianist]

It has been fixed now but I'll ask anyway since only now I have noticed this thread so wouldn't vaccum leak make it idle higher as oposed to lower?

[Brianmoooore]

The engine should idle at low revs from the air that gets past the throttle butterfly, and then this is brought up to the correct idle revs by the electronics opening the ICV the correct amount.
The ICV on a M20 works on a different principle than the ones on most engines - instead of an electric motor acting against a spring, the M20 has what is effectively two motors, turning in opposite directions, and fighting against each other.
Try removing the ICV and plugging the hoses on either side, or plug the ICV itself and refit it. Does it still rev. at 500 RPM? If so, the ICV isn't working and is remaining shut, either because it just happens to be shut, is jammed, or is being powered shut.

Yes, a vacuum leak would normally raise the idle, but you don't know what bodges have been performed by a previous owner to try and fix it.

[IamStandingBehindYou]

The engine should idle at low revs from the air that gets past the throttle butterfly, and then this is brought up to the correct idle revs by the electronics opening the ICV the correct amount.
The ICV on a M20 works on a different principle than the ones on most engines - instead of an electric motor acting against a spring, the M20 has what is effectively two motors, turning in opposite directions, and fighting against each other.
Try removing the ICV and plugging the hoses on either side, or plug the ICV itself and refit it. Does it still rev. at 500 RPM? If so, the ICV isn't working and is remaining shut, either because it just happens to be shut, is jammed, or is being powered shut.

Yes, a vacuum leak would normally raise the idle, but you don't know what bodges have been performed by a previous owner to try and fix it.

Thanks for this, I'll try it tomorrow when I get the car back. The mechanic seems convinced now that it's a poorly adjusted AFM, but an ICV would make a lot of sense.

[Brianmoooore]

I presume he means the AFM bypass, not the AFM itself. This is an adjustment made at the factory and should never need moving, but as I said above, you don't know what previous owners/mechanics have been up to.
Make sure they mark the exact position that it is at now before they touch it, and it should only be permanently adjusted with a CO meter connected to the exhaust.

[IamStandingBehindYou]

I pulled off the AFM today and had a good look at it, I also checked resistance across its terminals as well as the terminals of the ICV.

The AFM is performing very strangely, and as the AFM door is slowly opened the resistance goes up and down like a yoyo. The closed reading is ~2130 Ohms and the full open reading is ~2380 Ohms, but as the door is moved the Ohms go from anything from 1950 Ohms up to 2890 Ohms.

As the door is opened slowly the Ohms will go up and down unpredictably and the same happens when it's being closed. On closer inspection, the top of the AFM (the black plastic part that can be removed to fiddle with the internals) has been very shoddily sealed with some sort of black silicone sealant, so it's clearly been opened by an amateur at some point and messed with.

The ICV showed resistance of 40.4 Ohms between the two terminals at the edges, 19.9 Ohms between the right terminal and the middle terminal, and 21.6 Ohms between the left and middle terminals (with the plug oriented so that the single plug shaft is at the top and the twin plug shafts are at the bottom). The ICV buzzes when the car is running and the valve opens/shuts when given direct battery voltage.

I'm reasonably certain that it's the AFM at the root of the problem, so I'm going to swap it out for a new/reconditioned one and cross my fingers. Has anyone encountered an AFM behaving like this before? I'm genuinely curious to open it up and find out what the hell is going on inside it.

[pianist]

I had it once, previous owner messed with afm on my car and it was over fueling badly and the guy in the garage did a good job to recalibrate it using CO meter like Brian mentioned above.

[Brianmoooore]

AFMs can, and do, go faulty, when the track of the potentiometer becomes worn or the sliding contact becomes tarnished, but your method of testing won't give conclusive results.
You need to connect a six or nine volt battery across the end terminals of the potentiometer, then monitor the voltage on the slider pin as the door is slowly opened.
The voltage should always increase as the door is opened, and must not drop back at any point.
The AFM signal isn't actually used at idle, although I'm fairly sure that a false signal from it, indicating the engine is above idle, will confuse the ECU.