RPM's dip sudenly while idling
 

I've stressed before that I really don't know much about cars. I just bought my first tool 6 weeks ago, so please forgive me for the stupid questions that follow.

When I am at idle, at about 600-700 rpms, I feel kind of a sudden jolt (not real big) and the engine dips about 50 rpms and comes back up. It happens about 50% of the time when stopped for more than 10 seconds. Usually at lights, not stop signs. I replaced my spark plugs 2 weeks ago when I did the valve cover gaskets, So I don't think that's it. There is no CEL.

1-Unfortunately I don't know what a misfire sounds, looks, or feels like, but could that be a misfire?

2-If it is a misfire, can I get Autozone to check for codes to tell me which cylinder is misfiring?

3-If it's an ignition coil, can it be fixed, or should you always replace one that is broken?

4-If I need to replace an ignition coil, would you recommend a new one, or getting one from a salvage yard?

5-If I get one from salvage, how can I check to see if it's good before I buy it and take it home?

6-If I am off base thinking it's a coil, is there any chance the IACV is messing up?

7-Regardless of the answers, should I just take it to check for codes every time I don't know what the problem is?

8-Will it throw codes even with no CEL?

Try cleaning the throttle body, IACV, and MAF first. You should also check the TPS with a multimeter. All the instructions are in the "How to" section..

You have a coilpack that's going bad. You're feeling an occasional misfire. Chances are that when you replaced your spark plugs, you accidentally partially broke a coilpack reinstalling it (easy to do on the rears).

Does it happen when your air conditioner compressor is coming on? There's a fast idle solenoid that's supposed to make the IACV open up when the AC compressor comes on, but after the temporary dip you'll see the tachometer end up a little higher, like 700-750 rpm, if that's what's causing it.

I wonder how the engine knows it's at a stop light and not a stop sign? ;)

There are codes that won't light the CEL, but enough misfires in a certain period of time will light the CEL.

Autozone will read the codes for you, but you've already progressed to the level at which you should just buy a cheap code reader. Then you can read the codes any time you want.

Ignition coils are usually replaced when bad. There's a procedure for checking them, involving measuring the resistance between the terminals. Buy new ones, unless you're just too broke to do that.

Misfire would light CEL. Try the cleaning. MAF, TB, IACV.

Misfire wouldn't light a CEL if it's not long enough. If it's one miss, it won't light.

I have the same issue and am waiting till I hit 100k to clean my MAF, TB, IACV as part of my routine maintenance. Should be right around spring time, which is perfect timing for a 'tune-up' for the summer traveling months.

NEVER buy used electronic components, part may or may not be slowly failing, giving you intermittent problems. Don't fall into "save money" trap, get a brand new part from a dealer or auto parts plus you will have a warranty on the part this way.

not always, my 97 went for several hundred miles shaking at stoplights and there was no CEL, and no ghosts, all I had is 0505 like nothing happened.

Best way to determine which coil out of 6 went bad is either:

1. Wait till coil dies to the point when it triggers CEL (again, you may go for several hundred miles on a slowly dying coil, which will give you all the symptoms, but not CEL). Once CEL is on, hook up a SCAN tool or perform a "screw" procedure, which is described in haynes manual in detail. Also, you can ask Autozone or Advance auto people to pull the code for you. The code will show you the probelm cylinder that needs coil replaced.

2. Procedure requires 2 people if your car shakes only under load (gear is in D or R). Have your assistant put the car on Reverse with brakes pressed. I recommend it to be on R not on D because if assistant accidentally moves a foot off brake pedal you know what happens next. Do not rely on emergency brake, it may or may not hold, you never know and better be safe than sorry. Pull the plugs one by one and notice performance difference- if the car stops doing intermittent shakes you got a problem coil. Important: there is a lot of misleading info on this forum about this procedure- some people will suggest you that when there is no difference in perfomance you got a bad coil. NOT TRUE. What you really need to watch for is for intermittent shakes- if intermittent shakes are gone, even if RPM drops, you got a problem coil.

If you replaced your plugs with anything other than NGKs, that could be your problem too.

He's having the EXACT problem I had, down to the tee. I guarantee a coilpack is going out/partially busted, and I bet that it's a rear one.

I pulled #1 (front passenger) and it was broken. Completely severed in the middle of the coil pack. I imagine it's not supposed to be like that. I will change it and update the thread to let people know if the dips stop.

Not related to AC. It happens with or without. And it doesn't go back higher than it started, just dips from like 600 to 550 and back real quick.

Maybe cars get smarter as the age?

Cheap? Elaborate please. How cheap? Where?

Please explode abbreviation. I don't know what brand I bought or honestly what type.

Thanks a lot for the replies guys. Since I'm doing the o rings on the rear timing case this weekend, the coil will be dust on the scales. If I get the car back together and it still runs, I'll let you know if it still misfires.

ill tell u what worked for me....Take coil packs out, pop the tube open, take out spring, use spring to scratch the contact point on coil pack box by twisting, profit.


becomes corroded. might work, might now, but it worked me of. I get them 90% less. Maybe once every 3 days.

Replaced coil #1 tonight. It was actually snapped apart in the middle lol. I will drive it tomorrow and let you guys know if it continues. I ran it for a bit and I think it's fixed, but I want to make sure.

Thanks again for all the suggestions.

Drove around today. No signs of misfire anymore. Easy fix for anyone with similar symptoms. It took me about 5 minutes.

-remove ornament cover with allen wrench (4 bolts)
-8mm socket and ratchet (2 bolts holding coil pack to valve cover)
-antiseize in the end of the coil to put over spark plug.
-don't over-tighten anything

NOOOOOOOOOOOOOOOOOO!
I was coming home today and noticed the dip again. Now I don't know if it really was fixed temporarily or if it just didn't misfire for a few days.

The dip is different now. Now, when I stop it idles fine for 5-10 seconds. Then it dips back and forth quickly from about 550 to 500 to 550 over and over until I hit the gas. It does the same thing in park, but it idles a little higher. When I use electric components like windows, sunroof or the like while idling the rpm's dip even lower (not sure if this is normal or not).

Anyone have any ideas? Any chance I have a bad coil? Or maybe I put too much antiseize on it? I'm lost. I'm taking it to Autozone to have them check for codes.

I was planning on hat this weekend when I do the o rings on the rear timing chain case. Hopefully that takes care of it.

<Please explode abbreviation. I don't know what brand I bought or honestly what type.>

NGK is a brand of spark plug. That's the ONLY brand that should go in Maximas. There are too many problems with other brands.

I did some more looking and listening today and went to autozone to get the codes checked. I have a P0325 "Knock Sensor Code". I will correct/restate the symptoms on my 97 I30 Auto Transmission:

-no roughness or noticeable stuttering, shuttering, or misfiring while moving
-at idle (in gear, AC off), it sits about 550 RPM's for 5-10 seconds after coming to a stop and then I feel a jolt and a drop down to about 500 Rpm's. Then it kind of moves very slightly between 500 and 550 constantly until I start moving and starts over if I stop again.
-When I use electrical components (i.e. windows, sunroof ...) the RPM's drop about 25-50 and when I stop using the component it goes back up. Normal?
-I don't notice any loss in power while driving, but I have driven corollas my whole life until now, so I'm pretty sure even on 2 maxi cylinders I would feel more power than I'm used to lol.
-While idling with AC ON, it seems to not have any problems. It idles about 700 RPM's and stays very steady.
-I got a P0325 today. They said it registered twice (not actually sure what that means).
-No misfire codes

The autozone folks said it's either the knock sensor or low fuel pressure and said to put some sea foam in the gas tank. I bought the foam for $10 thinking even if it isn't the problem it can't hurt.

Anyone able to tell me where I should start? I kind of have a feeling it's not a coil or spark plug since I don't feel any problems while moving. I don't know the tech part of things, it's just a hunch. Is the car supposed to idle higher than 550 RPM's with no AC? Why do symptoms disappear with AC on?

That's very similar to the problem I had, a shudder at low idle (in gear) when I was stopped. If I put it in park, it would go away, and it was fine while I was moving. In other words, it only showed up at low idle. That could be your problem--when you turn the AC on, the computer kicks the idle up to compensate for the increased load.

I replaced my Autolite plugs with NGKs, and that solved the problem.

Here is what I would check...
Fuel Filter... Replace it. I am sure its crazy dirty. You need to pull the fuel pump fuse and crank the car a little to get the pressure out. Remove the gas cap too. Its an easy replacement and cheap.
Clean the MAF sensor with MAF sensor spray. Its an easy cake job
Go to the dealer and buy a $3.00 IACV gasket and remove your IACV valve. Take it apart inside. There are 3 philips head screws to remove the little cover inside. Completely clean it out with carb cleaner. I gaurantee its REALLY dirty. Put on the new gasket and tighten it up. Totally easy job. The IACV really affects your idle and start up.
Replace the PCV valve. Its a cheap $4.00 part.
Go on Ebay and buy an OEM knock sensor for around $40.00 shipped. Spend about 30 minutes and install it. The trick to installing it is getting a flexible drive extension for your socket wrench. You won't have to remove anything but the one bolt holding it in.
After you replace the knock sensor, go to Auto Zone and have them hook the OBDII scanner up to it. It will still show the knock sensor code. Thats ok. Also... the guy at AutoZone isn't allowed to clear the code but he can tell you how to do it. its just a couple button pushes on the scanner.
That should do it.

Thanks, I did use cheapo plugs a few weeks ago and it seems that is about when I noticed it. I will change them this weekend.

I am going to clean the IACV this weekend while I'm replacing the timing chain guide and tensioner and the o rings on the rear timing chain case, and I'll probably do the fuel filter since I have to release the fuel pressure to get to the timing chain.

Thanks guys!

dan1el

Please post update latter as I'm too in same boat, I have yet cleaned MAF, Air filter and TB but no improvement...I am gonna try cleaning other stuff latter.

It also seems I am getting exhaust rich in gas (based on noting of gas smell), particularly when I am driving in town ( stop and go at low speed ), does anybody have any advise whether my case is any different for that reason ?? else I have all those symptoms what OP posted.

I had the same kind of up down unsteady rpm with my '97 161,000miles. So I cleaned all the ground points from rust/dirt and paint with a dremel tool. Each wire eye hole scraped and body paint. So that the flat washer of the ground is now touching bear metal on the car instead of paint. I read that all grounds are touching the car via the self tapping threads on each screw. So now I have better contact. After that I spot spray painted each ground screw with silver caliper paint I had around to help future rust around areas that I over scraped with the dremel and is not covered by the ground washer.

I also added some additional ground connections on top of each ground where I could.

I also used an entire can of MAF cleaner that could of helped as well.

It's at 185,000miles now and idles like a champ per my scanguage II.

I also changed the knock sensor (ebay $40.00) around 160,000 but it only cleared the check engine light and did very little to my idle IMO.

Speaking of knock sensor's there are two grounds to it that you need to remove and scrape clean. Mine were gunky with dirt. Google it.

Improve the grounds, it's cheap and it can't hurt.
my2cents

mines nose dives when i first start my car in the morning wonder why

Mine does as well. It started when the weather got really cold, but hasn't gone away as the weather has gotten warmer. The alternator went out and was replaced, but the stumble on start is still there. I'm chasing down options . . . I'm still wondering if it's related to something that may have gotten damaged when I hit a deer back in late November.

same. however I feel it may be a pack issue. As I get 1-2sec hesitation when I double stop the pedal in 4th or 5th.

dont forget to check the harness connectors too. They could also be faulty

Sorry for not updating recently. My car is now one of the infamous crank but no starters. Once I have it running, I will know if my plugs were the problem.

Still no start man....did u check out the CKPS POS and REF yet

Sensors are fine. I tested everything I could with my multimeter and almost gave up but I decided to try finding TDC and while cranking the crank shaft with a ratchet, it turned about half a rev and stopped dead then back the other way the same thing. My timing is off for sure cause the shaft should turn over continually without stopping. I just hope my valves are ok from all that cranking listening for symptoms. My brother in law is coming over tomorrow and we're taking the outer TC cover off again and will reset the timing properly and hope she starts when we get it back together.

im having the same problem.... i just replaced my plugs from Bosch Platinum Plus to bosch Platinum...and now i am having surging while in OD, horrible jumping and kicking if the A/C is on, when it is off it is less, and its Pissing me off.

EDIT: While i was pulling the hardest coil pack out...(Right Rear) it got stuck and i tugged on it a bit. idk if i might have broken it or not.

Sorry about bringing back an old thread.