I've noticed for the past couple days that there is a slight miss / hesitation when I'm at idle when the car first being driven. I don't know if it's really a "miss", but i can feel it only at idle and I see the RPM dips ever so slightly (from 600 to maybe 550) for like a 1/4 second. Everything else feels normal. Normal acceleration through the RPM range, no hesitation. It does clear up completely after I've driven it for about 10min. Honestly, it's subtle enough that I feel most people wouldn't notice, but I'm hyper sensitive about my car so I notice.

I did change both valve cover gaskets 3 weeks ago and it did not have this issue. From the research I've done, it could be the IACV needs cleaning (I didn't get to that when I changed the gaskets, but I did clean the throttle body). I would lean towards vacuum leak from changing the gaskets, but if it were that I would assume I would have felt it right after changing them. Lastly my crankcase ventilation hose is cracked, and I ordered a new one that should be here in a few days, I don't think that would cause this issue? Anyway, any help would be appreciated. Maybe I just need to run some injector cleaner through her and see how she goes.

 

So it seems that you did not have that issue before you changed the valve covers.

I could imagine a vacuum leak

1. Did you use new gaskets for the uim to lim.
2. The egr stuff
3 tb gasket
4 are all hoses tight.

how about connections to the the coils

 

I suppose I should be more clear. I changed the gaskets 3 weeks ago and have been driving it for 2.5 weeks without issue. Although to your point, I will check over the hoses. Yes I did replace the UIM gasket, the EGR gasket (although that one was a huge pain to get on and it probably got bent during the process, and the yes I replaced the throttle body gasket.

I just went out and shot a video of it from inside the car. Maybe I’m just being over sensitive, you can’t even really see the rpm gauge move. Maybe I’m just asking too much from a 20 yr old car! Lol

 

I have done all the under uim stuff.

my 24 year old car with 220k idles very smoothly.

retrace your steps. It's all to easy to miss something. Happens to all of us.

 

Here’s a link to the videos. In the longer vid it dips at the beginning. The short vid it’s maybe easier to see how small the rpm dip really is. Once again this only happens for like 10min. After that idle is perfect.

https://www.dropbox.com/sc/99qzdtthe...AekuRM7mvMOvPa

After doing some research on the forums, it could also be a coil pack going bad. I have 194k on her and all the coil packs are original.

 

Thought this over.

You saI'd this only happens as the car is warming up after sitting for a long time. But it behaves normally after that.

the iacv is there for controlling the amount of air the engine runs on during warm up.
A sticking valve inside it could cause that symptom.

I took my iacv apart when I had the upper manifold to deal with injectors and other stuff.

The parts were cleaned with spray cab cleaner, a tooth brush paper towels, perhaps a q tip or two.

The task is fairly simple. I removed some goo which could cause sliding parts to stick.

Replace the gasket.

​​​​​​

 

Thanks a lot for your help JvG. You are definitely one, if not the most helpful on here.

I ended up getting the codes and it had 2 P0235 codes. Grabbed a new knock sensor, installed it today and problem seems fixed.

 

Well.... It wasn’t the knock sensor. It’s still doing it and it’s seemingly getting worse. It will now do it even when it’s fully warmed up.

I’m grabbing all new coils and throwing them in today. While I’m in there I’ll take a look at the plugs and see if any look bad (I just replaced them 3 weeks ago so I would assume I could see what coil is bad based on the spark plugs) If it’s not that I’m guessing injectors and I’ll take it to a mechanic for that. I’ll let you know incase anyone comes across this thread and has the same issue.

 

Lethal, firing that parts cannon gets expensive.

first of all, the knock sensor seldom sets a code all by its self. It shows a code when whIle it's just fine. It shows a code when something else has a problem. I had a bad and cracked knock sensor.
The only real symptom was that it didnt perform any better on premium gas than it did on regular.
Once that was replaced I noticed a significant increase in performance on premium gas. You might try premium once your other issue is fixed.

 

Just grab an old timing light and attach the inductive pick up around the coil pack pigtail and view each cylinder by watching the light! Any and ever miss is visually indicated! This method is cheap and easy! Once you find the missing coil pack swap it with a good one! If the problem swaps as well it's the coil pack! Be sure to inspect the coil pack boots for rips and tears. This allows ignition leakage to the spark plug tube instead of the plug itself! My advice to all is to inspect the plugs as well, any signs of heavy salt & pepper is detonation, sooty is rich, pale white is lean, chocolate brown is perfect! If you don't know your mileage on the plugs just change them! I've actually used E3 spark plug and they worked well delivering performance and good gas mileage. The final thing that'll really help your ignition perform consistent is applying dielectric grease to the coil pack boot and spark plug engagement area! This well help seal and contain the energy to the plug even if submerged in water or oil!

 

Lethal.

I said that the miss at idle is probaby the iacv.

yet you replaced the knock sensor.

now you want to replace all six coils. And probably with non oem ones. Which don't work as well as what you have now.

Please tell me why you did not clean out the iacv.

I like to figure out what the real problem is before spending money.

The iacv can be fixed for FREE.

 

IACV won't cause a miss it'll cause it to idle higher from my experience...This dude sounds like he digging a rabbit hole going with non OEM coil packs (A No No that's been Preached to the Choir forever)...GL folks!

 

Could be leaking injectors as well!

 

I had a different 98 i30t back in 05 that would miss ever so slightly at idle and only at normal operating temperature. It was so subtle that it never set off the SES light. Turned out being a bad coil pack.

 

Cmax,

Lethal said that the miss occurs during the warm up phase. The car does not miss once warmed up.

So either a faulty coil or injector magicly fixes it's self once the engine is warm, or the engine is not getting enough air. Due to the iacv. I'd say this is similar to over-choked carbs in the olden days.

That's why I think iacv. It's also a free and preventive maintenance project which should be done sooner or later.

a free fix is a very good price.

 

Okay guys! I want to thank you for your input. I ended up buying a front a rear coil pack. First thing I did was pull all the spark plugs to see if 1 was charred any more than the others. No dice, they all looked great. The next thing I did was replace 2 (1 front, 1 back) start it, if it still missed I’d move to the next 2. Second set of coils I put in, it fired right up and idled perfect. So it was a bad coil pack.

I WILL replace the coil pack I got from the parts store with an OEM one. I just wanted to find the culprit. Hopefully this thread will be helpful to someone in the future.

JvG, the reason I didn’t clean the IACV is I just didnt believe that would cause a miss. In my mind it had to be something related to spark.

 

Lethal,

My iacv guess is based on your statement that the car misses when the engine is warming up.

Yet does not miss when the engine is warm.

Do I understand you correctly?

So I'm thinking that the coil or possibly injector fixes it's self by magic when it's nice and warm.

Actually I don't believe that at all.

I think it's relatedto the warm up process.
Which is controlled by the iacv.

My early years of car fixing involved cars with carburetor's . They used a mechanical choke to restrict air as the car was warming up. That would create a rich fuel mixture. Occasionally engines would stumble and miss because they did not get enough air.

The iacv has the same function as the choke on a carb car. It let's a certain amount of air through it so the engine can idle. Less air at first, to create rich mixture. Then more air for leaner mixture.

I think that the plunger in the iacv is sticking. Which means the engine is not getting enough air. That reduces rpm and makes the engine stumble. Eventually the plunger frees it's self, and the engine runs properly.

I can understand where you are coming from.

I'm about having a car run as well as it possibly can while still not spending lots of money if I don't have to.

So I personally would try a free fix. One which just takes my time. At best , that fixes my issue. Or at least I know that the item is working properly.

I'm thinking that you might spend a few hundred dollars when you don't have to. Only to learn that the real issue is something cheap you over looked.

I've been down that path. Learned the hard way.

Best wishes. And good luck.

 

Hey there JvG, to be clear it’s fixed. It was a bad coil pack.

 

ok. Glad it's fixed.

Did you replace one coil. or more?

I have not experienced a bad coil.

did you figure out which one based on the test CMax suggested?