The occasional hesitation/dip in rpm?s when idling.

Some background to give a clear picture of what�s happened and what was done. I noticed when I would get to a light, once in a blue moon, the idle would drop from the ~800 rpm down to ~400 for a split second, then come back up and be fine. Read a lot about the ignition switch causing phantom problems, which I was getting like door/dome lights coming on randomly. Replaced the ignition switch, all that stuff went away. Seems like it fixed the once in a blue moon dip in rpms. It did�for about 2-3 days. No check engine light, so I assumed needs new plugs and coils. On the way to the Indy to get the coils and plugs replaced, it dips, then the check engine light comes on. Perfect, no need to explain anything in detail, surely that�s related. Went to pick up the car and said �I guess that took care of the CEL.� Well, I was shown the CEL was for no signal to the SAI pump. No signal from SAI pump, and both banks lower than they should be. Car definitely runs better either way as the coils had small cracks and needed to be replaced anyways. Seems like after some reading, that was my issue with the dip in rpms given I know the coils and plugs are now new. Replaced the SAI pump with a generic one with good reviews and it idled perfect, test drove perfect�.for 2 days. Dip came back. CEL came on, this time just low bank values. Cleared the codes to see if it was fluke, got a dip this morning with it cold, but no CEL came on. So�what causes a dip in RPMS like that that doesn�t always throw a code? Did I get a bad SAI pump? Car runs phenomenal otherwise. Pulls really strong. No smoke or other weird hesitations anywhere. I only use Shell or BP premium, so it�s not the gas (too sporadic to be that anyways). Air filter is clean. It�s not throwing codes, so not sure where to go next. Vacuum leak somewhere?

Does the SAI pump actually run? If it seizes up - very common btw - it draws so much power from the alternator the engine bogs down for an instant.

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The new SAI pump I think is�it�s quiet and there�s no code. I wouldn�t think a new pump would seize up though???

Unplug the SAI blower and see if it clears up.

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No change in anything. Replaced the air filter, went with a different brand. Got a Carquest Premium paper filter from Advance...fixed the issue....for about a week. It came back. No codes until tonight where the air was 29*F. Codes were "insufficient volume in bank 1 and 2". It's got to be a faulty SAI pump right? It's the only thing that could make it throw an insufficient volume code right?

What year is your car? The secondary air injection (SAI) pump only pumps air into the exhaust system to help light off the cats, and has nothing to do with engine air intake. The SAI system will throw specific codes when faulty, however it does not affect engine running. What specific P codes are you getting? Have you cleaned or replaced the MAF sensor? I ask the year because if it is an early car, idle is most affected by the Idle Control Valve (ICV) on the throttle body.

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It�s a 2004 so it�s not an ICV. the codes I got the first time it came on were: Not sure what the clutch thing was..but after replacing the SAI pump, I no longer get the P0418-04 code. If it does give me a CEL, I get the bottom two SAI codes. i haven�t cleaned or replaced the MAF sensor, but wouldn�t that give an MAF code?

U may want to swap or test the change over valve. Its the gray box thingy with an electrical and vacuum connection. If u r just getting the bottom 2 codes then its seeing the sai pump but the motor sensors r not getting the desired effect from it turning on. The change over valve must work and open the system for the sai air to get in.

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Looks like both of em need to be changed then. I�ll give that a shot an report back.

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I think there is only 1 change over valve for the system. I think u r getting 2 codes because it is reading the result of a sensor on each bank. I just think the sai air in not making into the exhaust to lean it out during start up. Also inspect the rubber hose in both ends to make sure its connected and not leaking.

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ahh, you�re right�I saw two changeover valves , but there�s only one for the SAI: https://rennlist.com/forums/996-foru...omponents.html thing is though�if that�s only used for circulation of exhaust gases, why would that cause the stutter/hesitation once in a blue moon?

May have nothing to do with your shutter or it can be causing a vacuum.leak but i doubt it. U may have 2 different unrelated issues.

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draws so much power from the alternator the engine bogs down for an instant.

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seems too coincidental to unrelated�..about 60-70% of the time, after that brief stutter the CEL comes on with those error codes.

I really want to post a thread with my experience on the Crank Position Sensor but there are so many. Most people will tell you that it causes a stall when warmed up/hot. In my case, I started out with idle dips exactly like yours and would stabilize after a second or 2. It progressed to stalling only when hot when the AC was off, to stalling on cold start as soon as you�d turn the AC on (or if it was already on), to stalling when cold, to stalling ALL THE TIME. After replacing it today, the car runs perfect. All this is to say, I suspected the wrong items based on just the idle problems such as yours.

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So there were no codes thrown during this ordeal? Trying to narrow it down and it also seems like this is a solution, along with the MAF�but I don�t wanna just start throwing more and more money at it seemingly haphazardly. I guess the good thing about doing that is you�ll have replaced all the sensors 😂

Actually, about a week out from the CPS sensor and while I�m not in the same boat as before with the random stalling, I am actually in the same boat as you. I only had CEL for O2 sensors below limit values. The idle still dips, doesn�t stall, will drop to about 500 and only when completely warmed up. It doesn�t do it nearly as often so I am not THAT worried but I do want to shoot for a perfect idle if possible. So, at least I resolved the stalling. To date, I�ve done this: - Replaced MAF - Replaced fuel filter - Cleaned TB and ICV - Fixed vacuum leaks and passed the smoke test (when the engine was cold) - Replaced CPS (biggest change so far was from this) Get a durametric, and start checking your fuel trims. I am not sure what �good� fuel trims look like though. Here�s what I�m doing next: - Read everything I can with Durametric and confirm it�s normal - Do a smoke test when the engine is hot and hopefully see that maybe there�s a vacuum leak when warmed up - Replace ICV, and maybe the throttle position sensor if all of the above checks out. I am not too worried about this though - I�ve seen idles drop on old cars, and never thought of it as being anything until this car came into my life. Phew.

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I think I may have gotten a bad SAI pump. I cleared the P0491 and P0492 codes that were present. After it sitting for about 45 minutes, I disconnected the SAI pump then started the car�no dip in RPMs after 2-3 seconds of it idling like it normally does� Interestingly, no CEL popped up either about the SAI pump being disconnected/no reading. Hooked up a a PORII and there are still no codes. I�m at school in the parking lot and it�s currently 52* outside�.I get done at 830 (5 hours from now) so the motor will be completely cooled by then and will definitely try to activate the SAI pump�we�ll see if the dip in RPMs was from the massive pull of voltage from the alternator when turning on the SAI pump or something else. I think the last time I had it unplugged it wasn�t completely disconnected and I pretty much just pulled it out of the being seated, but didn�t COMPLETELY set aside the plug, I just kind of left it there and it may have still be JUST ENOUGH connected to still work�. We�ll see in a few hours when the engine is completely cold.

Well, no dip during cold start. However, after driving for 20 minutes, I pulled into Chick Fil A, and it did dip one time when I pulled into the drive thru�otherwise, all other idles and stops lights it was fine. After reading a bit, I think the variocam solenoid seems like it may be an issue worth investigating. It gives the issues we�re both having, and given you�ve replaced all the other usual suspect, it makes me think it�s that�

U can graph the rpms and actual crank angle. This might tell u if the variocam is hanging up

When it dipped after 20 minutes drive after cold start, was SAI pump still disconnected? Did you get any codes set for no SAI function? Lastly, on a .2 (is yours .1 or .2?) I know the SAI pump runs more than at startup. For example, mine was accidentally left disconnected after some work I did. The next morning I drove to work, and after 30 minutes of driving, finally hit a stoplight. So that was the first time at idle post startup. At that time, the DME called for the SAI pump to run, instant code set. I pulled over, pulled codes, got SAI code. Looked at pump, noticed I left disconnected, reconnected it, cleared codes, no more issue. So, moral, SAI pump can run at different times. -Tom 2003 C2

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how do I to that? I�ve noticed the variocam engagement at ~3200 rpm is more abruptly activated than it used to be�or it could be my imagination lol Mine is a .2. SAI pump was left disconnected for that cold start and drive. It�s still disconnected. Oddly no CEL was thrown when I started and drove and I know it would have been used for that because the outside temps were in the 40s and the engine was completely cooled as it sat for hours. I haven�t put it on a scanner to see if it threw codes but there�s still no CEL. I haven�t driven the car since that post.

Not exactly sure how it reads in ml2 telemetry. On my scanner for the mk1 i could see "actual" crank angle. Its a value that would change around 3200rpm as opposed to the cam deviation number thats more of an average and doesnt change. Not sure what scanner u have but a durametric and my autel will see and graph the value as well as most shop scanners.

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Ah, I have PORII.

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Started up fine this morning, no CEL from the SAI pump still being disconnected after starting and driving. About 15 minutes into my drive, CEL popped up. Code was from it being disconnected, and the below value in bank 1 and bank 2�.no other codes.

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I bet at that 15 minutes mark you had reached a stoplight or a reason to go near idle speed? -Tom

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. Yup! Hit a stop light! Reset the codes, started right up�no issues. Then this afternoon, same thing, except when I checked the codes, there was only 1 code: �Low bank 1��no code about there being no SAI pump connected, and apparently bank 2 was fine lol. This is beyond frustrating lol.

Try unplugging the sai relay. It's in the relay rack behind the back seat. Might be a problem with the wiring?

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Gonna give that a try this weekend. I take it I have to remove the subwoofer box to get to it? SAI pump hasn�t been plugged in for a few days, no codes since the last time I cleared them. It was 28* out yesterday and no hesitation/dip or codes�