Ericjergs

97 EJ6 D16Y7 with Y8 intake manifold, manual transmission.

So to start, my issue is... on cold starts it will start fine and sit at normal cold idle range. Then after maybe 15-30 seconds, the car seems like it starts to slightly miss/have a rough idle and slowly start to die, but never fully does. As soon as it gets to around 4-600 rpms it will shoot back up to correct cold idle and behave normally, this takes maybe 5-10 seconds from beginning to end. At any moment when it starts doing it, I can blip the throttle and it will immediately fix itself. The car is now hunting (not quite surging yet) for idle for a few seconds when coming to a stop, so I figured I need to start working on this issue before it gets worse.

When I first go the car car I had a bad surging idle. Trying to fix this I replaced the IACV with an ebay/amazon replacement. It ended up being intake manifold gasket. I'm thinking about just straight up buying new OEM IACV and seeing if this is the issue, and I can't find the original I took off.

What I've done... adjusted idle, set timing, a couple idle re-learn cycles, bled coolant, cleaned everything during my Y7 to Y8 intake manfold swap (& replaced gaskets), changed plugs, and distributor cap & rotor.

Plans are to replace wires, since I'm not certain when these were last done, but they look to be in good shape. I also have a fuel filter that I bought to just replace as maintenance whenever I got around to it.

I've read headgaskets slowly leaking coolant into the combustion chamber will do something similar, but the fact that I can immediately make the symptoms disappear by blipping the throttle makes me think the headgasket isn't the issue. I'm also not losing any coolant, and this doesn't happen every time, especially if I don't let the car idle long before driving away.

Couldn't find very much regarding this specific idle issue, let me know if you know of a thread that discusses it.

Thanks everyone!

muellersfan

Did the IM come from 99-00 D16Y8?

CEL codes?

Clean IACV and TB; adjust throttle cable; and then go from there.

Ericjergs

It's an auto 96-98 I believe. So the IACV goes on the throttle body, and the only ports I needed to block off was the cruise control. Swapped throttle rotor, as I kept my Y7 throttle body.

I did keep the Y7 throttle cable though and as far as I know it is adjusted correctly? Are you just talking about the slack or is there something more here?

No CEL, TB was re-cleaned a week or so ago with no change. I can re-clean the IACV to see if it makes a difference.

Ericjergs

So cleaned IACV, and was bleeding the coolant and the bubbles never really stopped.
They were intermittent, but after an hour of bleeding and thermostat opening 4-5 times, smaller ones would still pop up.
I have access to a pressure tester to ensure this isn't an external leak sucking in air, but from what I know this is usually a headgasket leak letting in exhaust gases. Might explain weird idle and would also explain the rough idle at cold start. Still think it's weird it goes away after the slightest touch of throttle, but who knows.

Haven't had a chance to see if cleaning the IACV did anything, as soon as I finished bleeding j left for vacation and haven't touched it yet.

What do you guys think? Anything I'm missing?

muellersfan

Rent (free) a block tester kit from an auto parts store.

Thoroughly clean the entire TB, and also adjust the throttle cable as per service manual instructions.

Ericjergs

So I'm 2 for 2 for no issues at cold start after replacing plugs and wires, TB was cleaned thoroughly only a few months ago, and re-cleaned a couple of weeks ago. Only does it in the morning, so I'll know more as the days past.

I'll look into getting a block tester to see about the headgasket letting exhaust gases into the coolant. I won't be able to test for a few days though. One thing I did notice though...When I was changing the plugs, from what I could see, the top of the pistons had no coolant on them. Everything looked fairly dry in there after sitting for 4 days.

Can a headgasket let IN oil/coolant but not let OUT exhaust gases? (if that makes sense)

Thanks!