I had a intake gasket blowout on cylinder 1 that I apparently had been there a while, so I decided to do all of the usual maintenance while I had the intake manifold off. Clean Throttle body, clean IAC, replace vacuum lines, new PCV, plus, and new FPR. New gaskets for IM and TB. I did remove the fuel rail as well. I did take off the Throttle Position Sensor to clean the throttle body well and I took photos and marked where the position was.

I got it all back together, fired right up but idled at about 2000rpm. Later it started surging every 2 seconds or so and stayed like that. I rechecked as much as a could but I cannot figure out what is going on. I unplugged the TPS and it ran like crap so it is working I suppose. I might have a small vacuum leak at cylinder three fuel injector maybe. What should I do next? I appreciate your help.

Hi,

I think your best bet is the throttle body like Grey245 is suggesting.
The engine is definitely getting more air than it normally would and the easiest place to do that is through the device designed to do that, the throttle body.

What 245 is suggested is maybe the stop screw has moved?
Especially, If it wasn’t tighten enough to take a stiff brushing or something got bent just a hair with a thump on the inside plate and it’s not shutting all the way closed.
The amount of air is above the range of control by the IAC!

Did you replace the throttle body gasket too?

When you said you removed the throttle position switch, it sounds like you got a little over zealous with cleaning, but all, for good reasons, to keeps solvent out of the TPS.

I don’t know how much farther you took this cleaning escapade. I hope you didn’t pull the shaft out?
Some carburetors and alike have shafts air seals mounted inside the throttle body and carburetor dipping sauces ate those up!
On those you don’t want to mess with Venturi to plate alignments either.


If it’s not the issue suggested above, then, the surging is probably being caused by the IAC not being able to respond quickly enough as maybe you may have moved some gunk farther down inside of it.
The IAC on these cars has a spring loaded return so the ECU is signaling for it close because the TPS says it supposed to be at idle. The ECU has limited options, to cut the fuel injectors pluse widths or adjust the spark timing to reduce idle speed.
Either will cause surging and its very fast in doing this.

I agree with Art Benstein that checking for a vacuum leak with a spray around the intake runners or injectors will not affect idle speed changes for the extra fuel as the stuff can be compensated very quickly by the idle control system.

I have imagined using some engine oil, to lay in or around the injectors pocket around, as if it should instantly disappear to the inside, But only then, if you have an injector O ring leaking.
At the same time, an idle difference or a quick blip, might happen?
I have tried this myself, but I have never found a leaking injector to know if it this works at all!
It’s just my imagination until I do get one, but at the same time, I’m not going to make one to prove that theory! (:-)

Intake gaskets most generally leak from the lower sides or the bottom of each runner because oil vapors rest there the most. This is over the joints when the engine is off.
So thereby, cooking themselves down into the gasket materials over time so a “substantial” oil/fuel resistant material is required.

The jury is still out on how thick that joint should be, in order to minimize its exposure or how to achieve sealing during expansion and contraction.
Plastic manifolds are on the scene now! Combined with coolant water jackets too! Whoa Boy, on the gasket lives there!

It’s these warpage conditions that invariably happen over “time” is the test!
Volvos engineering seems to favor a thicker material over some of newer aftermarket brands.
240 have been known to go up too or over 200K on many cars!
This is only because IMHO Volvos suppliers meet their requirements and prices while all the time against the thinner competitors ideas!

So I gravitate in that direction of putting forth good materials into a product, makes a good product!

Experimentation has its limit but it brings innovation and it also has to be balanced like everything else.
Volvo’s early reputation has proven they knew something about balancing for the many years of producing the 240!
It looks like a mass of the newest Internal Combustion Volvos, will never get the chance to be tested as long, if future electricity plans go forth!
Vacuum leaks related to performance will disappear too?

What fun is that? (:-)


Phil

Thank you for the response. So I did not remove the shaft, but I got one of the smoke machine testers and I found a leak int he accordion intake hose, but there was a good deal of smoke coming out of where the shaft passes through the throttle body, on both sides. But prior to me doing all of this, I did a smoke test and I found the spring side of the TB leaking and also I found the blown out intake gasket. The car wasn't doing any high idle or surging then. So I am at a loss understanding how after replacing the IM gasket which seemed to be a big leak, could I have that large of a vacuum leak through the TB and that hose that would case this. It seems like I screwed up something on the Throttle body by removing the TPS. I did clean the IAC. It is still working. I unplug it and it runs much differently. I put the TPS at the exact same tilt that it was at. I went ahead and ordered a new IAC just for fun, but I wonder if it is the TB doing it. I hear an audible click when it is in idle position. Of course I ordered a new accordion hose too. I siliconed it last night, as a temp fix and when I get home I am going to try and diagnose it some more.

The car idles at 1500 when cold and then then when it warms up some it starts surging.

Yes, because of all parts replaced, these are the adjustable AND critical ones and the adjustments may have gone out of spec. just because of the disassembly alone.
This might have been aggravated if in the past, a gunked up system was "corrected" for by adjusting the stop screw. Not a good thing to do in an LH system.
I suggest you follow the procedures written down in the excellent FAQ on this very site before you do anything else.

Reset you Idle Air Control valve. There should be a wire you can ground to do this.

Hi,

FYI a reset is only on the LH systems with an IAC prior to 1989 when they had three terminals.
TheECU uses them to move the motor back and forth.

The later ones have a spring return that always hold the IAC in the closed position when there is no power.

In his case the IAC can be closed but too much AIR is going around the IAC and if the accordion hose has a split then that is unmeasured intake past the AMM.
This alone, causes mixture issues too!

Yep, that entry point for air control is a handful of trouble, if the throttle body is not set right!

I'm confident that He will get it fixed!

Phil

Thanks for the response Phil. I have the Bosch TPS. Here is what I did. I Set the idle screw to where it is just touching the spring return stop and then made another half turn into the stop. I then turned the TPS counter clockwise until I heard a click and locked it down. Now when you open the throttle just a hair, there is a click. Shouldn't that be set correctly now?

Before adjusting the TPS, make sure base idle is correctly set to approx. 500 rpm.

Buried in the FAQ here on the BB I found this procedure with the correct order and specs:

Setting Base Idle Specs and TPS on Bosch LH2.4-Equipped Cars . [Adapted from Volvo Service Manual 32043/1]

Cleaning the Throttle Body: See the discussion in Engine:Performance for more information

Adjusting the LH2.4:

1. Adjusting Idle Linkage Rod.

Ensure that when the cable drum is pushed off its endstop with a 2.5 mm feeler blade, the gap between throttle lever and adjustment screw is from 0.1 and 0.45 mm. (This is the adjustment screw that mounts on the throttle lever, not the adjustment of the larger nut that attaches the lever to the throttle plate shaft). To achieve the above spec, adjust the throttle link rod (ball-socketed connection rod between drum and throttle lever)

2. Checking the Throttle Body (Plate and Throttle Position Switch) Adjustment

Connect an accurate tachometer then warm up the engine. Let it idle in Park with a/c off. Pinch off the hose between the air intake and the IAC valve (don't damage the hose with something sharp!) Idle speed should drop below 500 rpm, or the engine may stop: both are normal. If idle speed does not drop, adjust as below.

3. Adjusting the Idle Speed

On the front side of your throttle body, there is an adjustment screw. Loosen the lock nut. Start the engine and turn the adjustment screw until idle is 480-520 rpm. Switch off the engine and tighten the lock nut while holding the adjustment screw so it doesn't turn.

4. Checking the TPS Adjustment.

Check the gap between the adjustment screw and the throttle lever with a feeler gauge. Insert a .45mm feeler gauge. There should be no click from the Throttle Position Switch on the rear side of the throttle body when the throttle is closed. Then insert a .15mm feeler gauge. There should be a click from the TPS when the throttle is closed. If these are incorrect, then adjust as below.

5. Adjusting the TPS.

Loosen the TPS adjustment screws holding it to the throttle body. First turn the TPS clockwise (away from the electrical connector) until it stops. While keeping your finger on the throttle disk so it won't move, turn the TPS counter-clockwise (toward the connector) until you hear or feel a click. Continue turning until it stops, then tighten the screws. Go back to step 3 above to check the adjustment.

Hey Grey245,
This is a response that I sent to Art in another chain above that you have commented on as well. It is about my high idle... Can you let me know your thoughts too...

Art,

So even with the idle stop screw OFF of the TB, linkage disconnected and the TPS engaged it is still idling high at about 1200-1500. It still surges some too (its an M47) so I am at idle a lot.

If I can turn it by hand (further closing the plate) and make it idle down to maybe 400 rpm (barely running) wouldn't that suggest that the spring isn't closing the plate all of the way? I think that is why blipping the throttle can lower it sometimes. What can I do? Should I screw with the spring? I need to replace the shaft seal as there is a vacuum leak anyway on the spring side. All of the standard procedures have been tried.

My thoughts are that you should fix the vacuum leak on the throttle shaft seals.

Did you go through the "Don't Panic" part of the Engine Tune and Performance" of the FAQ?
It deals with idle problems and the causes.

There's this bit on a TB vacuum leak that seems to correspond to your symptoms:

"Idle Surge, High Idle, Poor Idle: Vacuum Leak [Inquiry:] Idle surges at times between 1200-1600 RPM when car not under load. Idle Control Motor? Other?

[Response: WBain] You have a vacuum leak. Check all lines especially at the throttle body. Also if it's a turbo, look for a bad intake manifold gasket.

Intake Manifold Gasket Leak. Mine has had a very rough idle. I checked the FAQ and cleaned the throttle body and checked for leaks in the hoses. I was finally able to isolate a leak in the intake manifold gasket. The propane test didn't find the leak. The only way I was able to isolate the leak was with the mechanic's stethoscope with the probe removed and only using the tubing to get very close to the gasket and follow the contour of the manifold. Replaced the gasket (approx. 2 hours) and the car runs fine.

[Tip from Gary Goms] Vacuum leaks can be easily diagnosed by several methods. I believe the safest and easiest method is to use a modified mechanical stethoscope to listen for vacuum leaks throughout the system. To modify the stethoscope for locating vacuum leaks, replace the probe with a length of plastic hose or fuel line. Alternate methods include listening for a change in engine speed while spraying propane or aerosol carb cleaner around manifold and vacuum connections. The various brands of smoke machines are also very handy diagnostic aids to use when attempting to locate vacuum leaks at the manifold-to-cylinder head gasket, throttle body shaft, throttle body-to-manifold gasket and vacuum hoses.

[Tips on reassembly of TB shaft spring:] I carefully took the spring off the side of the throttle body, noticing that it was under tension... one full turn, but alas... I forgot to note if it was under tension one full turn CLOCKWISE or COUNTER CLOCKWISE. [Response:] The throttle body spring, attached to the throttle body lug that goes into the throttle body and points out from the throttle body to the radiator goes CLOCKWISE! The spring has a little bent-out stop that catches under the idle adjustment screw. You put the spring on so that catches... twist the dang thing one turn clockwise, put your nut on, attach the throttle control rod and it's done.

Special Note on Use of Solvent Cleaners. [Larry Carley, Brake and Front End Magazine, Dec 02] Using conventional aerosol carburetor cleaning solvents on fuel injection throttle plates, for example, can be an extremely expensive mistake. Although strong solvents instantly dissolve gum, varnish and carbon from throttle plates and bores, they also dissolve throttle shaft seals, throttle position sensors or (when applicable) the Teflon from the air inlet horn! Nevertheless, specially formulated throttle body solvents do as good of a job without causing potential driveability complaints. Most are also good for cleaning delicate import carburetors for the same reason. Unlike killer carb cleaners, throttle body solvents don't cause comebacks by eating away at delicate switches, potentiometers and neoprene diaphragms found on import carburetors. Most throttle-body aerosols also spray in the inverted position for cleaning hard-to-reach components.

HI,

Well a half turn is way too much!
I would have the screw do exactly as you described to just touch the lever.
Then I like only giving it another little twist about the width of the screws slot for the screwdriver.

All you want to do with that screw is to provide a resting spot to hold the plates outer perimeter surface from being hammered shut into the walls of the bore by the return springs pressure.
We want the plate to close in such a way that it's up and touching without pressure to tightly close it so it cannot get jammed or deformed from a sudden rapid release from a wide open position.

The cable pulley above operates without any stops even though there are tabs on the pulley they are not used. They were used and there for earlier micro switches on K jet systems and alike come up in design of the 240s.
They got replaced by the Bosch shaft switch TPS and LH system.
So you want to make sure that the cable itself has some slack going over the pulley drum too.
This allows for the engine to rock and shift on its rubber mounts.

Don't get to wound up worrying about the linkage rod in between.
As you will see ,its adjustable, but its set purpose is to keep the throttle pulley tabs away from their stops above so all can get to close the throttle with the return spring that's pulling the foot feed cable.
There might be a specification for the tab space distance, someplace in old manuals, but it really is, "Don't have it touch!"

Bottom line the plate is too be or get closed just as important as they now do inside the IAC!
The older IAC's were held closed electronically and this presented a "minor" safety issue that was addressed after around 1987-8, I think?
The throat size of these IACs, are or were, intended to be self limiting by design, so, that's why I say "Minor."

Still a "high idle" is a little unnerving in any case!
All the LH systems use the ignition system RPMs and a computer program to set the idle speed of 750 rpm.
The days of a higher idle speed due to air conditioning loads are instantly adjusted by these IACs.
In the early years of say around 1983-4 LH 1.0's we saw all the electrically controlled vacuum "leak" valves, disappear!
Mainly because that leak was behind the AMMs and raised havoc!
I imagine that Emissions was the motivation between several groups of design desks!
A push for Lower "idle emissions" was the total goal, so no more 1000 RPMS for the A/C load allowed.
Shortly there after, we got ridiculous, with heated Oxygen sensors to speed up process, when lab technicians got more persnickety! (:)

Yep, back up the screw a little bit!

Phil

In answer to your question--what to do next? You sort of self-answered in saying you may have a small vacuum leak at one injector. Use a spritser bottle of water (safer) -- or spray carb cleaner (effective but not as safe as water) to confirm a leak - and check all of the injectors as well as every joint in the system. - Dave

Can an injector seal cause that much of an issue?

From where I am to where the car is I can't say if one seal will cause your issue but it can certainly make a difference and without checking all joints and points of air entry neither can you. A vacuum leak will cause the mixture to change--the FI system will try to compensate for the leak causing a fluctuating idle. You have to start somewhere and vacuum leaks would be where I'd start. - Dave

"I rechecked as much as a could but I cannot figure out what is going on."

Did that rechecking also include adjustments of the throttle plate and TPS?

Thanks for the reply. I did not check the plate. Wasn't aware of that. The TPS was put back where it was originally. I will have to research that.