Need help diagnosing a high idle

[ctfortner]

My (new to me) 5.8 EFI Volvo is idling high, around 1500 rpm, even after it is up to temp. Its a pretty smooth ide, not rough or jumping around.

I was thinking the IAC valve may be bad or previous owner may have adjusted the TB idle screw. It idles good, although high, and ran great on the water. Shifted slightly hard in and out of gear because of idle.

Today I ran it to temp and then disconnected the IAC, it stuttered briefly and died. Would not crank with it disconnected. Plug it back in and it is right back to idling 1500 rpm. Should it idle (even poorly) with IAC disconnected? I am wondering if someone before me adjusted that idle screw, or should I just get a new IAC vave and swap out and try that first?

I have not disconnected the throttle cable yet to see if that could be the issue, but this may sound dumb, but If the boat is in neutral, I have tried pushing on the throttle itself to see if it would idle down...but the throttle cable will not move forward or backwards when trying to do so at the TB by hand., while boat is sitting in neutral.

I made a video of it running and then dying, see if this link will work
https://photos.app.goo.gl/ewfrZQMDkfJDx4502

[AsLan7]

Hey welcome to the Cobalt chat forum ctfortner. So glad you found us!

The ECM controls the idle on your EFI motor. You may want to have a tech hook up a laptop to obtain some readings. It will help diagnose fuel pressure, vacuum leaks, tps info etc. Then you can troubleshoot a little better.

Any pics of your boat? I saw the engine video. Hope you can get this solved.

Again, welcome aboard mate!

.

[thunder550]

Welcome to the site!

What year is your boat? Can you hear/feel a difference in the idle speed, or are you just relying on the tach? Reason I ask...it's a fairly common issue for a tach on a boat to read high occasionally. Mine does it at the start of nearly every outing, I have to knock on the front of it twice with my knuckle and it goes back to where it's supposed to be. Let's rule that out as an issue first since it's a really simple solution.

[cmattj]

You'll need a scanner to see what the iac is being commanded for idle speed rpm . Is it being told 900rpm? etc ( that would tell you if the set screws been tampered with.)

On a throttle cable system (non DTS) it shouldn't die when unplugged unless there is some fail safe im unaware of. Possible why it wont crank after unplugged??. I would suggest having it scanned or throwing a Good Iac on it.

Hard shift is usually high idle but tachs as stated can be off. The money you'll spend having it scanned may saving you throwing parts at it.

[Big Block Power]

Do you have a extended warranty? That should prob be covered?

[ctfortner]

Hey, I guess a few more details would help huh. For some reason I thought I had posted my boat and pics before, but I see I have not. It is a 1995 220, with the 5.8. I bought it from a guy last month. He took to a service place and had them summerize and do an engine check, change oil, and even do a water test. It all checked out other than a busted oil pressure gauge and P/S was 3/4 quart low. I went an picked up there and before buying, we threw it in the water and I drove it around the lake for about 30 minutes. Hole shots, WOT, cruising, etc. Ran great, but we noticed it sounds like the idle was high and sure nuff, the gauge was reading aroun 1500.

The engine was replaced in 2011 with a (said to be) new Jasper engine. I know it is a Jasper in there because it is stamped by them with a serial number and I called and got the details on it.

Now, since I made that post this morning, and before I read yall's posts here, I have done the following. I disconnected the throttle cable, removed IAC valve and cleaned with TB cleaner, cleaned inside TB with spray and a brush. Put IAC back on, fired it up and she just purrs at 1500 rpm without missing a beat...so, no change.

Engine was hot by then so spraying solvent wasn't in my want to do list, will try on cold engine later today. I'm still thinking hard about that dam idle screw though. What now ? If it was a vac leak would the rpm bounce around? If it is a vac leak, would it be noticeable in running WOT on the water. I drove it before I bought it last month, performed flawless for 30 minutes, just idled high. No stutter, hesitation, stalling, nothing. It would be awesome to know what and how to adjust or check if the idle screw is in the factory position. Is there any manual that discusses that?

I don't think it is a tach issue, it definitely sounds a bit high, and on a cold start it is around 2000 RPM, and then will ease down to 1500 and settle in once warmed up. Has a slight "grind" to it going into gear, not real bad, just enough to feel it.

I would get a scanner, but where can you hook to a marine engine? I have done a little engine work here and there, mostly carbs, but this is my first marine engine experience. I have a laptop. I am in IT so I can handle that part if I knew what to get, unless its big $$$$

[ctfortner]

These are pics before cleaning...most of the black is gone on the TB now. I didn't really see a whole lot to clean on the IAC??

TB.jpg

IAC2.jpg

IAC.jpg

[cmattj]

You'll need a scanner to see what the iac is being commanded for idle speed rpm . I would suggest having it scanned or throwing a Good Iac on it.

The money you'll spend having it scanned may saving you throwing parts at it.

You had the iac in your hands so there's the first part you can throw at it.

OB ports for omc, ford, Volvo have certain location during rigging hidden and capped by weatherpacks. Unlike a car underdash.

[TommyTahoe]

Welcome to the site!

What year is your boat? Can you hear/feel a difference in the idle speed, or are you just relying on the tach? Reason I ask...it's a fairly common issue for a tach on a boat to read high occasionally. Mine does it at the start of nearly every outing, I have to knock on the front of it twice with my knuckle and it goes back to where it's supposed to be. Let's rule that out as an issue first since it's a really simple solution.

Welcome ctf,

I think your tach may be off as well... I listened to your video and the engine doesn't sound like its revving at 1500, but I'm no mechanic. When it almost died it still showed 1000, my thought is it should have shown less.

[2ridgebacks]

It's hard to say from the video, but the idle sounded close. Watching the belt looked good for an idle speed as well. At 1500, my belt markings are pretty much a blur.
You said the oil pressure gauge was changed, that means they were likely behind the dash. It's not unusual for a tach to have a switch that allows you to select the number of engine cylinders. Look the tach over well and make sure there is no switch and if there is, it is on 8 cyl.
You should be able to look at the screw on the throttle body to see if it is contacting the throttle plate arm. If it is, turn it out to see if it changes anything. You could also disconnect the battery and let the PCM die. It will recalibrate the IAC when it starts.

[Big Block Power]

Ridge is correct. Check the back of the tach make sure it's set on 8cyl. I didn't listen to the vid. Without a scanner you won't be able to see where the iac counts are at. Remove your throttle cable. Is the throttle closed. They're mouht be a throttle stop afew not sure on a Ford darn 4 letter word. But I can tell you changing my idle speed screw which should really never need to be turned. That screw should be set to a certain voltage at closed throttle. Again when I turned mine the idle changed but the computer took over and made the iac put the idle right back whereit wanted it. So turning that screw won't fix your issue. Buy a cheap timing light with a tach on it and connect it and see what you have. Also a vacuum leak will make it idle high and no you won't notice that at wot. You can remove both battery cables and connect them together for 15 minutes then reconnect them and it will relearn the position. Let it idle for 10 minutes.

[Mr Hahn]

On the back of the Tach there's a switch to change between engine types. Even if it's in the correct position (8Cyl as said above) rapidly cycle it through all positions several times. There might also be a calibration screw on the back, if there is don't mess with it. My tach started indicating about 600rpm high and I had to do this to make it work again. There's probably some corrosion on the contacts and this might help it read correctly for a while. Also, check what rpm it reads at WOT. If this is just a Tach issue then it will probably be showing above max rpms at WOT. My 7.4L should max at 4600 rpm, when my Tach drifted off it started showing 5200 at WOT which probably would have blown my engine if it had actually gotten that high.

-Nate

[cmattj]

You can remove both battery cables and connect them together for 15 minutes then reconnect them and it will relearn the position. Let it idle for 10 minutes.

Global resetting GM guy right there!!

[AsLan7]

Hey, I guess a few more details would help huh. For some reason I thought I had posted my boat and pics before, but I see I have not. It is a 1995 220, with the 5.8. I bought it from a guy last month. He took to a service place and had them summerize and do an engine check, change oil, and even do a water test. It all checked out other than a busted oil pressure gauge and P/S was 3/4 quart low. I went an picked up there and before buying, we threw it in the water and I drove it around the lake for about 30 minutes. Hole shots, WOT, cruising, etc. Ran great, but we noticed it sounds like the idle was high and sure nuff, the gauge was reading aroun 1500.

The engine was replaced in 2011 with a (said to be) new Jasper engine. I know it is a Jasper in there because it is stamped by them with a serial number and I called and got the details on it.

Now, since I made that post this morning, and before I read yall's posts here, I have done the following. I disconnected the throttle cable, removed IAC valve and cleaned with TB cleaner, cleaned inside TB with spray and a brush. Put IAC back on, fired it up and she just purrs at 1500 rpm without missing a beat...so, no change.

Engine was hot by then so spraying solvent wasn't in my want to do list, will try on cold engine later today. I'm still thinking hard about that dam idle screw though. What now ? If it was a vac leak would the rpm bounce around? If it is a vac leak, would it be noticeable in running WOT on the water. I drove it before I bought it last month, performed flawless for 30 minutes, just idled high. No stutter, hesitation, stalling, nothing. It would be awesome to know what and how to adjust or check if the idle screw is in the factory position. Is there any manual that discusses that?

I don't think it is a tach issue, it definitely sounds a bit high, and on a cold start it is around 2000 RPM, and then will ease down to 1500 and settle in once warmed up. Has a slight "grind" to it going into gear, not real bad, just enough to feel it.

I would get a scanner, but where can you hook to a marine engine? I have done a little engine work here and there, mostly carbs, but this is my first marine engine experience. I have a laptop. I am in IT so I can handle that part if I knew what to get, unless its big $$$$

.

So we have some clarification needed here. Your first post said that this is an EFI motor which normally refers to fuel injectors which inject fuel into each of the cylinders (SFI, MPI, etc.). However, you are showing pics of a throttle body.

Being that this is a 1995 boat, it’s most likely electronic throttle body injection.
If you clean a throttle body, many times the ecm will still remember the position of the throttle BEFORE the cleaning and try to adjust the idle higher when the cleaned throttle closes further to it’s new position. The electronic control unit is trying to compensate for the new position of the butterfly valve. Sometimes this will eventually work itself out after a number of hours.

I believe you are having difficulty shifting because of the high idle.
A marine tech with a Mercruiser or Volvo diagnosis program on a laptop can check all this. ...and we would love to see pics of your craft.
Btw, here is the tech troubleshooting our MPI motor. The Merc (or in your case Volvo) software program will tell you quite a bit about your engine.

.

[Ytmsn]

Ewww. Everytime I see this pic A7 I automatically think

"cha-ching"

Welcome to the gang CTF. There lots of good info here!