GregBBRD

The fact that you can change the idle speed through the vacuum hose that is connected to the power brake venturi seems odd. You should confirm that the power brake booster holds vacuum, because one side of the venturi is attached to the power brake booster....and unless it has a leak, that is "dead headed" vacuum, once it gets pulled down.

The other side of the venturi is connected to the "Y' fitting that goes into the boot that connects the AFM to the intake. It's almost impossible to not get that particular "Y" attached properly, since there are two large ends and one small end, however, people can do strange things. Another thing to check is to make sure that the "tiny hole" in the small port of that "Y" hasn't been drilled out....I've seen that, several times. Finally, look carefully at that "Y". They are known to crack.

Pagnobito

I can hear the click hot and cold and also see it switch at the ECU pins by pressing the throttle, also hot and cold test so I don't really think my TPS is bad but I'll change it out anyway as it's not that expensive in the whole scheme of things. The cables are adjusted OK.

I've vacuum tested the brake booster several times, it's all good. I'm pretty sure the Y connector is good and not leaking but it's a valid point and I'll check that over when I lift he intake to swap the TPS.

This whole thing started because my idle was too low on a cold start and eventually I had to press the throttle to keep it running until it warmed up. After I changed the ISV this has happened, I've put two new idle valves on and even tried my old one so maybe I did something that first time around but I've done several intakes before and I find the only tricky part is getting the hose that runs from the oil filler back to the elbow under the air meter difficult to locate without binding. I've obviously removed this one several times, maybe 6 times in all looking for reasons this is happening. It seems signal/electrical rather than a leak as I'd think a leak would be immediate and not something that would switch after a few seconds.

matt968

Since we both have the exact same problem, Just following up since I received my remanufactured LH by JDS from Ott's Performance. Put the LH in the car Saturday. Drove it for about 38 miles total. After the first 10miles the idle seemed fine every time I came to a stop and put it in Neutral to check....until I got home and pulled in the garage and then it was back to the 800-900 rpm. Fortunately I do not own a gun or I would have shot it.

Today I drove about 30 miles and after it got to operating temperature the idle was around 800-900 again. One other thing I tried after coming to a stop and placing it in neutral, I shut the car off and would immediately restart it and the idle would be back to normal 675....until I drove some more and came to stop again and checked then it was back to the 800-900 range again. I tired this twice, with with the same results - the idle would be correct on the restart.

I know my TPS is not "trigger-happy" there is plenty of slack in the throttle body cable. I too have checked continuity directly at the pins that connect to the LH and it switches fine.

Will follow up if I get more information......or a gun to shoot it.

Pagnobito

Thanks for the update, I feel your pain!
I'll be using a Sharktuner on mine this week to see if I can log what is happening, let's hope it shows up something that can help us both.

matt968

I just went outside and checked the timing. Stays around 10 degrees from cold to hot.
It does not feel like an air leak. In fact, I can introduce an air leak through a vacuum line and it can compensate for it and hold idle.

Is there anything related to the transmission that sends a signal to increase rpm’s? While it was hot, I pulled it out of the garage and drifted down my driveway without touching the throttle. It felt like it was drifting down hill in first gear. I popped it into neutral and idle was correct. Put it back in drive and drifted further and faster (maybe 10-15mph) until it shifted into the next gear. Stopped at end of driveway, popped it into neutral and it was idling high!

SteveG

Not transmission related, but the A/C on should increase idle. Also, I believe the Temp II sensor's purpose is related.

Pagnobito

The transmission is guided by vacuum, throttle position via cable and gear selection with an override on kickdown, it's not going to affect engine speed. I haven't intentionally introduced a leak to see what happens to mine.

The AC doesn't increase engine speed very much. Temp 2 tests out fine on my car.

Pagnobito

I borrowed a ST2 and appropriate ECUs to attempt to see what's going on.
There are three data log files attached which can be loaded into a spreadsheet and from there create a line chart. I have edited them to the relevant part. Those with an understanding of the log files can see what's happening but it doesn't tell us why as everything seems steady and normal except MAF signal increasing as idle speed increases.

From a cold start (warm up 1) the engine idles higher and gradually decreases but then seems to hit a point and increase idle very quickly and stay there.
From a hot start (hot start) the engine quickly settles about normal and after a few seconds or as of today as much as 123 seconds increases idle which is repeatable on each hot restart.
Within the ST2 software if I disable idle control and run the ISV about 34% the idle will stay steady around normal speed. In fact toggling this make the engine run normal speed (idle control disabled) and jump back up when I turn idle control back on.

I have tested the brake booster for vacuum and actually left it overnight under vacuum and it didn't leak. I blocked the fuel vapour line, idle still increases. I blocked the line to the transmission for the hell of it and it still increases.
With a vacuum gauge inline with dampers and on hot engine start it quickly climbs to 18 In/Hg and just before the idle increase it drops to 16 or 17 In/Hg before going back up to 18 as the idle speeds up. It's like pressing the throttle except I haven't, the TPS stays in idle all the time (on the ST2 software monitoring).

if I block the hose to the brake booster with the venturi in place (with everything else standard) the idle will increase by itself. If I remove the venturi and block only the intake plenum hose and leaving the MAF elbow hose open the engine rpm doesn't increase and the vacuum remains steady at 18 In/Hg
The intake has been removed again to inspect the Y piece in the MAF elbow, it's not cracked and it's connected the right way and the little hole to the venturi is there so it's not that. I was hoping so much that it was considering blocking air that route stops the problem.

It certainly seems like a vacuum leak or additional air causing the idle increase and a sudden and measured amount. I can't blame the brake booster as it does it without it connected and even though for some reason I can stop it by blocking the air from the MAF elbow to intake there's nothing in those lines that can alter the amount of air passing through them. I can also stop it by software disabling idle control and turn the high idle on and off in that way!

I'm still no closer to working out what's happening.

Taguid

Baffling! I wish I had an answer for you.

GregBBRD

Make sure no one drilled a hole thriugh the butterfly to allow extra idle air to pass through the butterfly when the idle stabilizer wasn't working....pretty common.....actually, way too common.

The other way to accomplish this is to re-adjust the idle stop screw on the butterfly....not as common, because it is more difficult to reach.

Monitor and record both the idle stabilizer percentages and the voltage from the stock O2 sensor from cold start to warm running. (Everything hooked up.)

Very minimal idle stabilizer opening percentages could be causing your problem....too much air getting past the butterfly while the idle stabilizer is working at a minimum value.

matt968

MIne was doing the same thing. Starting from cold and letting it sit and warm up, when it reached operating temp. (fans would come on and off maybe two or three times) it would change idle on its own from normal to around 900. I replaced the venturi and now I can let it sit and warm up and it will hold idle - no problem. But when I drive it the idle will change to the higher idle. I check it by coming to a stop and placing it in neutral. When I changed the venturi I made sure to drive it 25+ miles and at all rev ranges and shifted manually a few times too. I wanted to make sure the LH "re-learned" its parameters. I'm wondering if that re-learn procedure is what helped the LH.

Can an O2 sensor that is intermittent or bad cause the idle to increase? Or along those lines, can an air leak on the exhaust side but prior to the O2 cause the sensor to read lean and increase fuel and therefore idle?

I ordered a new TPS and will put it on later this week or weekend and will report back. It worked for "Taquid" and I'm hoping it works too.....even though mine appears fine by scan tool.

Pagnobito

A little history. bought car in 2012, It had bad knock sensors, vacuum leak and air leak traced to bad butterfly bearings. It was easier for me to replace the lower part of the intake during the refurbishment. It ran well after that until last year when it became more difficult to keep it running from a cold start until it wouldn't at all without throttle. It was left over winter. I replaced the ISV, no longer have the cold start problem and now I have this problem. It could be something I did so I went over everything again checking for air leaks and so on, replaced the ISV for a second time and then the CPS caused a hot start failure. The CPS has been replaced now. I've done a couple of intake refreshes before with mistakes learned from.
I'm sure the butterfly is correct and has not been altered. In any case I would expect any air leak at all from anywhere to cause an immediate high idle from engine start on a hot engine and not something that's happening after a few seconds running?
It makes little difference if the O2 is connected or not in terms of the high idle. If I disable it on the fly idle increases very slightly and drops back when enabled again. I must have not checked the O2 adj on the logging page, I'll try that when I next run the engine.
I wouldn't know what a normal idle percentage looks like, do you know roughly where it should be?

I'm considering fitting a WB02 just so I can monitor this. I know it takes a while to heat the standard O2 before it goes closed loop but disconnecting mine doesn't stop the idle jump on a reset LH.

FredR

I see nothing unusual in your data files and I see no correlation between the rpm increase and the MAF output- the values bob about a bit but that happens on mine albeit I have no checked my values.

The clue here seems to be the venturi assembly sucking in false air. Remove the venturi assembly and pull the venturi nozzle out of the body. There is an O ring seal in body that may have failed or there is a crack in the body somewhere.- I suspect that may be passing air into the plenum. On mine the fit felt a bit slack so I put some RTV sealant on the walls.

Pagnobito

The venturi is good, no leaks and I tried another one too, both the same.

You are right the RPM bobs about a bit but it also increases at one point and stays there idling around 900 under normal conditions. Blocking air through the venturi stops it happening as does disabling idle control. There is additional air but probably not false as MAF signal increases with idle speed therefore the air is measured. The log is showing what is happening but not why. I've checked every hose and connection on the venturi plus brake booster and none leak. However, blocking that line makes the ISV operate in a different position? It's an unknown why airlfow increases and at a certain point during warm up or after a few seconds when warm. It's not maps or ECU as I'm using different ones now with the sharktuner and it still does it.

GregBBRD

Sharktuner is looking for a wideband O2 sensor hooked up through Sharktuner. I don't need/want that. I'm looking for a voltage reading from the stock O2 sensor when it is hooked up. Poke a hole in the signal wire and hook up a digital volt/ohm meter. Cold, it should start out at .5 volts. As the engine warms up, it will wander up to about .7 volts. Once the O2 sensor is warmed up (about 90 seconds) the voltage will fluctuate pretty quickly (every second or two) between .2 volts to .8 volts.....constantly going back and forth. (The O2 sensor is a detector that the brain uses to keep the mixture in the correct range. The fluctuating voltage is caused by the brain slightly increasing and then slightly decreasing the fuel delivery, depending on what the O2 sensor is telling it.)

You can use Sharktuner to monitor the Idle stablilizer percentage. If the stabilizer percentage is too high (80%) it is at the top of its ability to open and add more air. Conversely, if the percentage is too low (20%) the idle stabilizer is shutting down as much as it can and can't go lower to reduce the amount of air going into the engine.

I'm trying to help you get to the bottom of where the excess air/fuel is coming from, by using data from the engine.

BTW....there's another "invisible" air leak that happens in these engines. Right on top of the water pump is a black solenoid that opens to vent the charcoal canister. They fail and will stay open all the time. If the "secondary" valve over below the overflow tank fails (and the "Y" in the passenger fenderwell fails, which is super common), you will have a huge vacuum leak that you will not see with a smoke tester. The quick way to start looking at this possibility if to disconnect the hose that runs between the primary and secondary valves, at the valve above the water pump (non engine side) Run the engine. If you 'feel" vacuum leaking through the valve itself, that is wrong. The valve should not allow vacuum to pass, when the engine is running at idle.....except for a few seconds when it is first started.