'97 SL2 RPMs drop below normal when slowing

[macinmypocket]

Hello everyone! I've been browsing around the forums for the last year or so, but I finally made an account to ask for some help.

My manual 1997 SL2 with 190k miles has started to dip RPMs below idle, down to as low as 400 any time pressure is released from the gas pedal, bounces back up to 1000-1100 RPM before dropping back down to normal idle at 800 RPM. Here's a video I took: youtu.be/HB9dl3rE0aI

I've scoured these forums for answers, and have noticed a couple people having the same issue, but so far nothing has worked for me.

(For example: 1997 SL2, 5 spd, DOHC. What I am describing happens at normal operating temperature.

In slowing down when approaching an intersection, I will push in the clutch in anticipation of stopping. If I was at higher than cruising RPMs when the clutch is engaged, the RPMs will drop to around 600 and then rev back up to 1000+ before settling down. Then, when I am at idle (sitting at stop light), the idle seems to be right at 810-830. After 10 seconds or so, I will feel the engine ever so slightly shudder. Nothing major, but I've been watching the tach drop to around 780 or so, and then it pops right back to 810-830.)


The list of things I've done so far is:

Replaced PCV Valve
Replaced engine coolant temp sensor (though with another resin tipped one, couldn't find a full brass one, but the original one seemed to be in perfect condition when I removed it)
Replaced air filter
Cleaned throttle body
Cleaned EGR valve
Changed oil
Checked for loose/cracked hoses and subsequently tightened/taped them up
Reset PCM after all of it

All of which I've seen as potential solutions to the issue I'm having, but none of them seem to have worked. The engine sure runs a little smoother and quieter now, but this problem still persists.

Any more ideas? I'm confident that someone here can help!
I'll make sure to go rep all of the incredibly useful guides and posts that've helped me this past year while I'm waiting. Thanks everyone!

[adventureoflink]

While you had your throttle body off, did you also clean the IAC valve? This'll cause your RPM to dip like this.

As for replacing an ECTS with the resin one, that shouldn't be.. I'd run and not walk from that place. All ECTSes (OEM/dealer or aftermarket) should be brass tipped by now. As to what condition the old one was in, by any chance, did you also check the connector for green corrosion?

[macinmypocket]

Originally Posted by adventureoflink

While you had your throttle body off, did you also clean the IAC valve? This'll cause your RPM to dip like this.

As for replacing an ECTS with the resin one, that shouldn't be.. I'd run and not walk from that place. All ECTSes (OEM/dealer or aftermarket) should be brass tipped by now. As to what condition the old one was in, by any chance, did you also check the connector for green corrosion?

I did clean the IAC valve while I had the throttle body off, I forgot to add that to the list. I'll go hunting for another ECTS tomorrow, I too was surprised that I could only find resin ones, but I figured c'est la vie and got it, but I'm not opposed to looking for another. Thanks for the reply, any more ideas?

[adventureoflink]

Originally Posted by macinmypocket

I did clean the IAC valve while I had the throttle body off, I forgot to add that to the list. I'll go hunting for another ECTS tomorrow, I too was surprised that I could only find resin ones, but I figured c'est la vie and got it, but I'm not opposed to looking for another. Thanks for the reply, any more ideas?

Only other thing I can suggest is R&R the IAC valve and see if that works (but then again you have a manual, it _might_ be the clutch but I'm not 100% sure; I only own the automatic saturn that comes complete with the floor shifter, eww. ).

[macinmypocket]

Originally Posted by adventureoflink

Only other thing I can suggest is R&R the IAC valve and see if that works (but then again you have a manual, it _might_ be the clutch but I'm not 100% sure; I only own the automatic saturn that comes complete with the floor shifter, eww. ).

R&R the IAC valve? I'm not sure what you mean. I could always try just sucking it up and buying a new one if necessary.

Oh, and it's interesting that you mention the clutch, I replaced that 4-5k miles ago, the whole flywheel, disk, pressure plate and throwout bearing, along with replacing the ancient fluid in the tranny with some sweet amsoil fluid.

[adventureoflink]

Originally Posted by macinmypocket

R&R the IAC valve? I'm not sure what you mean. I could always try just sucking it up and buying a new one if necessary.

Remove and Replace the IAC valve. Take the throttle body back off, take the IAC valve off, put a new one in, then re-install the TB.

Originally Posted by macinmypocket

Oh, and it's interesting that you mention the clutch, I replaced that 4-5k miles ago, the whole flywheel, disk, pressure plate and throwout bearing, along with replacing the ancient fluid in the tranny with some sweet amsoil fluid.

Good deal. I was kinda hesitant on suggesting replacing the IAC valve since you cleaned it but the symptoms were still there. however if you replaced it and the symptoms didn't get any better I didn't want you to be out $30 for playing parts bingo either...

[macinmypocket]

Originally Posted by adventureoflink

Remove and Replace the IAC valve. Take the throttle body back off, take the IAC valve off, put a new one in, then re-install the TB.

I'll give it a shot, I need to keep this baby runnin'.

Originally Posted by adventureoflink

Good deal. I was kinda hesitant on suggesting replacing the IAC valve since you cleaned it but the symptoms were still there. however if you replaced it and the symptoms didn't get any better I didn't want you to be out $30 for playing parts bingo either...

Occasionally parts bingo is the only way to get things done.

[Brendo613]

Mine has the same problem, even after a complete engine rebuild. Don't waste your money buying an IACV - mine's blocked-off completely in favor of a manual idle setup. Though it's that way for years, the idle surge problem still persists on mine. Have you solved yours? I've definitely had enough of this anomaly

[macinmypocket]

Originally Posted by Brendo613

Mine has the same problem, even after a complete engine rebuild. Don't waste your money buying an IACV - mine's blocked-off completely in favor of a manual idle setup. Though it's that way for years, the idle surge problem still persists on mine. Have you solved yours? I've definitely had enough of this anomaly

No, unfortunately, I still haven't gotten this solved. It doesn't happen every time I'm in the car, but it still does it occasionally. To be honest, I haven't put any further work into investigation or money into parts, but if anyone else has suggestions, I'm definitely open to trying them!

[Brendo613]

Hehe understood. I've been living with this for a while now myself, but after a bottom and top end rebuild, it's time to sort out allll these little faults. Best of luck to ye

[macinmypocket]

Originally Posted by Brendo613

Hehe understood. I've been living with this for a while now myself, but after a bottom and top end rebuild, it's time to sort out allll these little faults. Best of luck to ye

If you get your car sorted out, let me know! I'm still up to trying things! Best of luck to ye too!

[macinmypocket]

Turns out it was the spark plugs. For anyone else having this issue, give that a try!

[Brendo613]

What ones did you put in? Congrats btw

[macinmypocket]

Originally Posted by Brendo613

What ones did you put in? Congrats btw

NGK Coppers. Some of the best plugs you can buy, and they're about $1.99 each. Real bank breakers, they are

[Brendo613]

well right on, more mac in your pocket at that price