Dear Fellow Brickboarders,

Hope you're well. On start-up the engine idles at 800 revs/minute. As the engine warms to normal operating temperature - temp gauge needle in the center - idle speed climbs to 1,500 revs/minute.

Thinking that corrosion might cause this rise in idle speed, I applied Deoxit to clean the idle air control valve (IACV) connector. No change.

Is the root problem an internal fault in the IACV, such that as the engine warms, the IACV malfunctions?

Wouldn't a vacuum leak cause a steady high idle, rather than a slow rise from normal to excessive?

I've replaced the engine coolant temperature sensor.

I hope to have the benefit of your insights.

Yours faithfully,

Spook

Dear Spook,

May this find you in good spirits.

I suggest you (1) be sure the TPS is providing the ground to the ECU when your foot isn't on the footfeed by back probing the ECU pin 2 (orange wire?) with an LED test light and then, if that is working every time, (2) be certain the high idle air is being provided by the IACV by blocking the bypass hose.

(1) The TPS "click" can't be trusted after almost 30 years to guarantee electrical function.

(2) Throttle wear and adjustment error can provide idle air beyond the ability of the IACV to close it off.
--
Art Benstein near Baltimore


"People that can use a test light, meter, a scope, and talk to the consumer without being mean to them can do very well in this growing industry. I've been an electronics tech for 30 years so I know just how much fun this electronic stuff is." -Dave dl242gt

Dear Art Benstein,

Hope you're well. Thank you, for your guidance. Am I correct to infer that a failed Throttle Position Switch (TPS) - by not providing a ground to the Engine Control Unit (ECU) - misleads the ECU to conclude that the throttle is closed, so causing the ECU to direct the IACV to open?

Can I use a Digital Volt-Ohm-Multimeter to see if the TPS works? If so, should I see 12 volts at pin 2, when the engine idles? If there's no voltage at Pin 2 during idle, should I conclude the TPS has failed?

This problem arose suddenly a few months ago, i.e., there were not periods of normal idle followed by intervals of high idle.

The factory-original TPS (I have car's records from new) does not owe me a penny.

May I replace a VDO TPS with a Bosch unit?

Thanks again for your help!

Yours faithfully,

Spook

"This problem arose suddenly a few months ago, i.e., there were not periods of normal idle followed by intervals of high idle. "

This is a good clue indicating to me you will not need to go out and buy an LED test light, which is much better than a meter for catching something intermittent. Yes, a voltmeter will verify the TPS.

In a Bosch system, the TPS closed-throttle circuit will show about 5V when the throttle is opened, and near zero when closed. Most external functions in Regina are configured to match the Bosch, even pin-out, so I expect you should see the same. The idea is, to verify the switch is working, you see the voltage change.

A common misconception has the idle air control valve "closed" or "not operating" when the throttle is open, but the fact is, the valve is always under the control of the ECU, regardless of throttle, and it does not close. The difference is the feedback from RPM to regulate idle speed is only enabled with the throttle closed.

By providing some troubleshooting information, I'm hoping to save you from assuming you need to swap in a new VDO IACV, which may indeed be the cure, just in case the expense and trouble of finding one is not necessary.

"May I replace a VDO TPS with a Bosch unit? "

I have no idea. Someone with 7/9 experience will tell us, I'm sure.
--
Art Benstein near Baltimore

What Thomas Edison's Mother might have said to her son:
"Of course I'm proud that you invented the electric light bulb. Now turn it off and get to bed!"

Dear Art Benstein,

Hope you're well. When last I worked on this car - a few weeks ago - I neglected fully to re-seat the Throttle Positing Switch (TPS) wiring harness connector. I found this error today, when I went to disconnect the TPS, as you suggested, to see if that would help matters. Once I seated the connector on the TPS, the idle stabilized at a tad higher than normal (perhaps 800 revs/minute (RPM) versus 700 RPM. I'll adjust this, on a day when temps are higher.

Thanks again for sharing your analytical insights, without which I'd still be at square one!

Yours faithfully,

Spook

Hi and good day to you Spooky Jay,

"idle stabilized at a tad higher than normal (perhaps 800 revs/minute (RPM) versus 700 RPM. I'll adjust this, on a day when temps are higher."

Sorry, Jay, your idle is not adjustable as such. For all LH and Rgeina systems, it's determined by the ECU using purple smoke, magic mirrors, the CPS rpm sensor, the block temp sensor and whether or not the AC compressor is engaged.

The FAQ talks about idle adjustment, but it's actually base idle adjustment. For LH 2.2, there's a base idle adjustment screw (black plastic knob) to adjust the amount of air bypassing the throttle plate -it's adjusted with the IAC forced closed by grounding a wire. There is no equivalent in LH 2.4 and Regina systems which use a different IAC where at rest the spring loaded valve is in the mid-open position rather than in the fully closed position as with LH 2.2.

The other aspect of setting base idle is setting the amount of air getting past the throttle plate in the closed position. Once set at the factory it should not need adjustment, but still worth checking occasionally in case someone has disturbed it (there's usually a drop of blue paint as an indicator). Adjustment is done with the idle plate stop screw on the left side of the throttle body and held in place with a lock nut. Note that the FAQ only describes this under LH systems. Regina adjustment is the same as for LH 2.4. There are two procedures for adjusting base idle with the stop screw. The one described in the FAQ under LH 2.4 involves removing/blocking hoses and setting the base idle at 500 rpm, but it's often difficult to achieve a steady idle at 500 rpm and you need a much more accurate tach than the dash tach. A far simpler method, and as used by many Volvo techs, is to loosen the TPS, hold the throttle plate closed with one hand and advance the idle stop screw until it just touches the stop and you can feel it about to open the throttle plate, then advance 1/4 turn more (1/2 turn for LH 2.2 throttle bodies with the lever and microswitch) and lock in place. In all cases, the throttle body needs to be throughly clean, especially the edge of the throttle plate, the central throat area and the small air holes (remove the brass hose nipples for full access and to ream with a fine wire or 1/8", as I recall, slightly undersized drill bit.

Many people adjust the TPS just past the click point. As long as it's not on the hairy edge, this is usually adequate. Proper TPS adjustment is described in the FAQ under LH systems using a feeler gauge then adjusting for the click. There are actually two specs, and it's not based on LH or Regina, it's based on whether you have a Bosch or VDO TPS switch. The VDO TPS procedure is exactly as in the FAQ, a .25 mm feeler inserted at the stop screw then turn the TPS counterclockwise just to the click and secure, locking luid recommended. The Bosch TPS swicth procedure is simpler, you don't use a feeler gauge, you just hold the plate closed, adjust past the click to end of travel and secure, locking fluid not mentioned. This is all from the Volvo TSB on the topic.

There are other specs mentioned in the TSB, including centering the throttle plate on it's shaft. The plates is centered with the idle stop screw backed right off annd adjusting the brass screw to center the plate for an even amount of light all the way around when looking through to a light source. The throttle shaft should also not extendtoo far such that it may bottom in the TPS switch and bind -a 22mm +/-0.5mm spec is mentioned for how far the shaft should extend out of the throttle body. Some people used to take that opportunity to knife the edge of the throttle plate at an angle (you can find diagrams on performance sites) and file off the tails of the brass screws (peaning the screws to lock them) in order to theoretically reduce air turbulence past the throttle plate, but I think we're talking a 1% improvement at best -I once did it to my 16-valve for amusement, can't say as it made any difference.

It's been asked before whether you can use an LH TPS switch in a Regina car. TPS switches for Regina systems are often not listed on parts sites or are listed as not available. As far as I can tell, yes, you can use either a VDO or Bosch switch with either system, but I can't confirm that myself. The mounting is the same, the connector appears to b the same, the function should be the same (switch on close, switch on WOT, no sense for position otherwise), so I have no idiea what could be different. All that's different is the adjustment spec for VDO vs. Bosch switches as noted above and it's not overly critical. Someone can correct me if I'm wrong here.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Sorry for all the typos and rough spots in the above post. I was called away after posting before I could proof read and edit prior to the post being locked by the system. The information is generally correct otherwise.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

you can clean the iac valve w throttle body cleaner I beleive,,,if nmy spellllin is bad its cause my cat is takin dictattion,,,,I think just take it off & let the throttle cleaner dissolve the gunk,,& work the moving parts bac n 4th

you can clean the iac valve w throttle body cleaner I beleive,,,if nmy spellllin is bad its cause my cat is takin dictattion,,,,I think just take it off & let the throttle cleaner dissolve the gunk,,& work the moving parts bac n 4th

If you use the Volvo OEM hose, you can re-use your spring clips that secure the ends of each segment. If you purchase another brand with different OD, then buy new spring clips at a plumbing supply store (Home Depot, Lowes) in the small brass fitting section or on the Web. They are called "corbin clamps" or "spring hose clamps".
i JUST FOUND THIS!!

Dear Blindboy,

Hope you're well. Thanks for your comments. What I don't understand is why the idle rate rises as the engine's temperature goes from "cold" to normal.

If un-metered air is the problem, that should lead to a high idle rate from start-up. That's not so here: it takes a few minutes from start-up for the idle rate to rise from 800-900 to 1,500.

By the way, is the hose - to which you refer - the main air intake hose? I inspected that hose: it seems to be in fine shape.

Yours faithfully,

Spook

With Regina, the air is not "metered" ahead of the intake manifold, but the pressure is sensed.

Still, too much air passing the throttle would indeed cause the idle to be high, whether past the plate or bypassed through the idle valve. The gradual rise would occur normally in any case where the air is not getting regulated by a warm-up response of engine control feedback, such as the RPM-adjusted idle valve.

So, the approach I'm recommending is, first, determine if the ECU is aware that the idle speed needs regulating, or in other words, is the computer brain aware you're not holding the accelerator pedal down. Then second, if it is aware, is the brain able to do something about it, i.e. limit the air it sends around the throttle plate that is senses is closed.

Another, easier method to determine whether the TPS is working, since you are not getting erratic response, is to simply disconnect it. If it is unplugged, the ECU is going to assume the throttle is open. So if your symptom doesn't change when you unplug the TPS -- that is if it still gradually revs up -- you have your #1 part of interest.

--
Art Benstein near Baltimore

You can easily judge the character of a man by how he treats those who can do nothing for him. ~Malcolm S. Forbes

I think its because when the engine iscold rubber hoses & fittings are tight when the engines heats up they get loose/slack & let unmetered air get iN?/

Could it be that someone has attempted to set the idle speed via the throttle plate stop rather than letting the IAC do its job? It wouldn't be the first time. They may have set the hard stop so that it idled fine when cold but that would surely make it too high when warm. Maybe the throttle body needs a good cleaning along with a readjustment, including the throttle position switch. The following four scans from the Volvo Rex-Regina manual spell out the adjustment procedure. Note, as Art suggests, hearing the "click" isn't proof the switch is actually opening and closing correctly. An ohm meter connected to the contacts should provide verification of both the idle and full throttle switching.

Sorry for the poor image quality. (Second generation scans.)

I would ty & trACK DOWN ANYWHERE THERE WOULD BE UNMETERED AIR GETTING,IN LIKE ON THE BACK OF THE TPS?WHERE IT MOUNTS??ON THE THROTTLE SHAFTi THINK THERE ARE 1 MINISCULE THICK O RINGS THAT MOUNT ON THE THROTTLE SHAFT,,ANY VACUUM LINES THAT ARE LOOSE EITHER COLD OR HOT??i THINK WHEN NEW VOLVO HAD LITTLE SPRING CLIPS ON THOSE HOSES,,,i WOULD LOVE TO FIND OUT WHERE TO BUY MORE

Time to replace the AIC controller. Have you cleaned it out ?