Strange behavior

[socal pat]

I started the car as normal in the morning, but this time the idle wouldn't settle in. Wild wanderings up and down almost stalling. I turned it off thinking it was a major vacuum leak. Everything looked good so I started it again and it started to do the same thing again so I used the throttle to manually override the ECU's job. Well, once I hit the gas it went right back to normal and ran/idled perfectly. I took it out for a spin and ran/idled great. Tried turning it off and restarting....no problem. Now every time I start it from dead-cold it does this strange behavior. I can make it stop by simply stepping on the throttle and all is well until the next morning. Any ideas?

[Tom @ Fast Forward]

Pat,

Do you have a narrow band A/F gauge, rear O2 sensor eliminator, or any other device attached to the front O2 seensor? If so, disconnect it/them and see if the problem goes away.

[socal pat]

Nope. Just an AEM wideband with its own bung, and all O2's in place. You may be on to something though. I was running pig rich with the JRPC. Could be I have an O2 problem.

[Banshee]

I have the same problem with weather change. Happens in the first minute or so. Then everythings fine.

[J_Man]

Nope. Just an AEM wideband with its own bung, and all O2's in place. You may be on to something though. I was running pig rich with the JRPC. Could be I have an O2 problem.

When I had the stock ECU - it didn't use the O2 sensor for the first couple of minutes until the coolant warmed up a bit. This was in a '94, I am not sure how are the newer ones a programmed but they also should ignore the O2 sensor reading and be in open loop during a cold start

[Tom @ Fast Forward]

They are in cold start until the heater signal is up. Doesn't take but a few seconds on the 4 wire O2. The older 2 wire O2 sensors took until the exhaust heated it up.

The O2 in a 4 wire sensor is very high in impedance until it heats up. Sometimes if a device is wired in parallel, it causes the ECU to think the exhaust is rich and then the ECU pulls fuel to make it even leaner. As soon as it warms up, the effective impedance drops and the parallel device no longer has an effect. The symptom is lean during cold startup for the first couple minutes and then all is OK.

[J_Man]

They are in cold start until the heater signal is up. Doesn't take but a few seconds on the 4 wire O2. The older 2 wire O2 sensors took until the exhaust heated it up.

Not on my '94. Even after heating up the O2 sensor if the coolant was cold, the ECU was staying in open loop warm up mode for some time and running richer than stoich. At that point it is not using the O2 sensor signal until the coolant gets warmer or some timer expires, or I interrupt it by blipping the throttle. The newer cars might be different and go instantly in closed loop mode as you say.

[Tom @ Fast Forward]

Just curious. How do you know that the ECU is not looking at the O2 sensor once it is warmed up and trimming the fuel?

[J_Man]

Just curious. How do you know that the ECU is not looking at the O2 sensor once it is warmed up and trimming the fuel?

On the serial gauge of my wideband TechEdge WBO2A. With it I could feed to the stock ECU with whatever signal I want and see how it would react. It was quite easy to figure out when it was in open and close loops. It was funny that simulating going out of idle mode would make it go in closed loop mode even the coolant temperature was not up yet. The heater of the O2 sensor and the O2 sensor narrowband signal were all controlled by me - so I could tell the stock ECU whatever I wanted and see how it reacted.

This is only about a '94 OBD-I ECU. I haven't played feeding signals to other stock ECUs ...

[Tom @ Fast Forward]

Ah. I've done my testing on the OBD II and none on the OBD I. Could be the difference. I guarantee that the 05 hits closed loop or modified open loop in very short order no matter what the temp. On a 20F cold start day, it is in on 14.7 before I can get out of the driveway and I get in, start the engine and drive.

[socal pat]

Well guys, I should have known I was over-thinking the problem. After letting the car sit for 36 hours I took out my idle-adjust tool, turned the screw less than 1/4 turn and it started perfectly. When you have the Idle adjusted so that it just barerly keeps the IAC happy then it's easy to make it hunt. This is twice I've had this problem and both times I hit myself on the head for not seeing it sooner. I mean the car in general and the FFS kit have been running so flawlessly it HAD to have been something siple. Thanks guys for the help, and I'm glad I was able to give Jman and Tom some fodder for debate ;)

[Kyp J]

Well guys, I should have known I was over-thinking the problem. After letting the car sit for 36 hours I took out my idle-adjust tool, turned the screw less than 1/4 turn and it started perfectly. When you have the Idle adjusted so that it just barerly keeps the IAC happy then it's easy to make it hunt. This is twice I've had this problem and both times I hit myself on the head for not seeing it sooner. I mean the car in general and the FFS kit have been running so flawlessly it HAD to have been something siple. Thanks guys for the help, and I'm glad I was able to give Jman and Tom some fodder for debate ;)

Elaborate a bit on the idle adjust and why it helped. I have been reluctant to mention a similar problem since I had a worse situation when my hose to the valve cover was off. Now it is doing what you described and I can't find any hoses off this time. I bugged Tom about it privately and went back and forth troubleshooting till I told him "OOps, forget everything". Now he won't talk to me anymore. :oops:

[Tom @ Fast Forward]

LOL. Kyp, people will think you are serious. ;)

[Kyp J]

LOL. Kyp, people will think you are serious. ;)

Sorry, I am seldom serious unless it is just an informational question.

However, when am I going to find out about the IAC bracket? :ack2:

I am also going to post a question or 50 about the Pro adjusting. Would you rather have that in an email? I am still confused I think.

[socal pat]

Well this is not technical enough for the more pedantic folks in the crowd, but it is what I know from experience. The IAC tries to keep your idle at a certain point which is your ECU is looking for. It is up to you to set your idle mechanically to a rough level so that your IAC can fine tune it to the propper RPM. If the idle stop is way too high or way too low the poor IAC is just working too hard. It's kinda like picking up an object you thought was really heavy with all your might only to find it was hollow and fling it over your head. I didn't follow the "rules" and unplug the IAC, adjust, plug back in, and see if the idle changes. I just new I needed a tad bit more throttle at start up so the ECU wouldnt have to hunt so high and low with the IAC to find the spot it was looking for.

[Kyp J]

So if the ECU is telling the IAC to jack up the air to idle faster, it doesn't know the fuel needs a bit of jacking as well? Is it not looking at the O2 just after start (open loop), unless it is revved a bit, and then it does (closed loop) at least for a while, which it seems is the case?

Mine seems to go to stoich for while after goosed, then creep back to lean until it is really warmed up, then it seems to idle OK. This is all very odd.

[socal pat]

Well, watching my AEM whilst this was going on, the ECU had plenty of fuel at cold startup so even adding some air, it didn't need to add more fuel. My warmup AFR starts between 10-11 for the first ten or fifteen seconds then I can watch the ECU leaning it out like .2 at a time every 5 seconds or so until it settles at 14 or so. The whole process takes oh 4-5 minutes. This is all with no throttle input from me. If it is just getting going and around 11.5 and I fan the throttle it will hasten the process a bit and might settle right down at 12 instead of the 11.5 i started off with. But with the idle properly adjusted won't ever droop below the 850-900 it is looking for. If your throttle is adjusted too low it will droop to a level that freaks the ECU out so it will over adjust then you are too high so it over adjusts again and your poorly adjusted throttle stop will allow the RPMs to get low enough to freak out the ECU so it over adjusts.........

[Tom @ Fast Forward]

The ECU sets idle with timing, fuel and air (IAC). To see how much air is needed, it looks at the MAF signal and tries to preset the IAC. What can cause a problem is that the MAF is looking at total air, the "leak" through the BTB, the flow through the PCV valve AND the IAC. If your idle is perfect for a long time and then gets unstable, a good place to look is at the PCV. When was the last time you replaced that awesome exremely high quality $2 part? :) If it gets dirty, the spring gets weak from heat or any other minor problem it can make a big problem.

The IAC is uncontrolled and is the major source of metered but uncontrolled, idle air. If it is not consistant, idle will suffer.

[Tom @ Fast Forward]

Kyp, I am a couple days behind on emails. I apologize. It was a crazy week and I had two contract engineering patent jobs that had to get done on a deadline. I get about 50 emails a day and try to answer them as they come in. This week has been an exception. I have IAC brackets and you are welcome to one. I will shoot one out tomorrow.

I promise to take your name off my "Do Not Call" list as well. ;)

The best way to get to me if you need an answer quick is to call. I answer the phone day and night. :)

[Kyp J]

Kyp, I am a couple days behind on emails. I apologize. It was a crazy week and I had two contract engineering patent jobs that had to get done on a deadline. I get about 50 emails a day and try to answer them as they come in. This week has been an exception. I have IAC brackets and you are welcome to one. I will shoot one out tomorrow.

I promise to take your name off my "Do Not Call" list as well. ;)

The best way to get to me if you need an answer quick is to call. I answer the phone day and night. :)

Sorry about the paranoia. ;) I guess you can have other things on your plate besides incompetant shade tree mechanics.

email your phone number when you get a chance unless it is in this forum somewhere. I may call to get help with the SS I tried re mapping. I can't get out of this post to look for the phone no. since it will erase it like the last one I tried about Pro adjusting. I have problems with that too. :surrender:

[Tom @ Fast Forward]

LOL. Kyp, My cell phone number is in my signature for every post I make. :hammer:

[Serpico]

now that's funny...... :biggrin:

Don't feel bad Kyp J . At least you didn't do this.......

[Scuba Steve]

now that's funny...... :biggrin:

Don't feel bad Kyp J . At least you didn't do this.......

Has it made a difference? I sure hope so.

[Serpico]

Nope. I just ordered some longer tubing last night, so I'll probably have it installed next weekend.

I deserve a dope slap for not seeing that sooner.......

[Kyp J]

LOL. Kyp, My cell phone number is in my signature for every post I make. :hammer:

The font size with your phone number was too big. My brain filters out things that are easy to see. Works the same on logic. If it is simple enough for a 5 year old to understand, my brain tries to make it complicated.:confused:

[Tom @ Fast Forward]

He has a hotside and stgretched the 3" hose to reach his cold air box. It appears to be nicly kinked as it makes the turn. That should be a nice smooth radius. I am sending him a longer piece of hose today to solve the problem.

[Kyp J]

Well, I accidentally figured out the probable cause if my lean idle. I was staring at my blower today trying out my Zen troubleshooting and looked behind the hose to the bypass actuator. "What, no bright blue bolt?" I queried myself. The plug for the water injector was missing. When someone else had his go missing I looked at mine and it was there then so I forgot about it. It must have fallen out after I found the hose from the valve cover vent loose. It ran very good for at least one day. If I didn't know I am the cause of most of my problems, I would start getting paranoid and blame evil spirits. This was just evil coincidence.

A quick call to Tom has a replacement on the way today. I glued a patch over it and wired the bypass open.

Edit on 1/27. After taking everything out around the "missing screw" it turns out it wasn't missing after all. Just deeper in the hole where I couldn't see or feel it. It was plenty tight so good news and bad news. The bad news is now I don't know what the lean idle thing is except the things previously speculated. I did notice while changing the IAC location and re routing the vacuum and vent hoses, the IAC is completely closed. I don't know what that means if anything.