# Hot start issue. Very irregular idle



## blown020 (Jan 9, 2009)

I've been struggling with the warm start issue ever since I got the car running on Megasquirt, and although the problem isn't very consistent I was able to log it tonight. 
On hot starts where the coolant temp has passed the magical 160* mark, I have very irregular idle. AFR jumps wildly and the idle goes along with it, dropping down to 300 rpm and then up to 900 or so. At no point does the car feel like it's going to die, it just keeps doing this until the car has been driven for a couple minutes. 
my ase table is below. The portion during hot start when the o2 kicks in is below as well. 
ANY ideas as to what I may consider changing would be greatly welcomed. If you need me to clear up any values in the pictures that may or may not be easy to read, please let me know. I can see it fine on mine :/


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## mjleamy (Mar 16, 2004)

*Re: Hot start issue. Very irregular idle (blown020)*

What's your IAT reading look like? It may be heat soaking, which is a common problem. After you drive around a bit, it will read the correct temp as air passes over the sensor and cools it down.
Show a screenshot of the IAT please.


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## sdezego (Apr 23, 2004)

*Re: Hot start issue. Very irregular idle (blown020)*

I have had a similar issue since day 1. The ironic thing is that I had the same exact issue when I was running Digi with an aftermarket chip (NOTE: it never did it with factory chip and I tested back and forth to verify it was not something else).
The only thing that I can rationalize is the IAT sensor as mentioned in the above post. I noticed that mine really only happens on a HOT restart on a hot day. So, heat soak on the IAT would seem logical. Mine clears up after about 30 sec to a min after the car starts rolling...
I was never able to get a good log of the issue like you were. Def post the IAT log from that. I have a FP gauge, so I verified there is nothing funny happening with the pump or fuel.


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## blown020 (Jan 9, 2009)

*Re: Hot start issue. Very irregular idle (sdezego)*

Mine definitely takes longer than a minute to clear out, and it just happened a few minutes ago. Just drove over to the store and it's around 60 degrees out. 
IAT is there. 97 degrees. Red line. 
Notice that it leans out bad and then richens up and the cycle continues. I'm thinking that it is a heat soak condition, but after tonight, ionno. I may move the IAT closer to the air box, but I honestly think that'll make a difference.


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## mjleamy (Mar 16, 2004)

*Re: Hot start issue. Very irregular idle (blown020)*

Are you running an open-air element or closed? I would get an open-air element IAT if you aren't already running one.


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## ValveCoverGasket (Mar 20, 2002)

*Re: Hot start issue. Very irregular idle (mjleamy)*


_Quote, originally posted by *mjleamy* »_Are you running an open-air element or closed? I would get an open-air element IAT if you aren't already running one.

i second that, i dont know why anyone would bother using anything other than the open element sensor...
also, be sure to mount it somewhere in the intake plumbing, ideally in a pipe thats isolated from the engine by silicone couplers. ive never had very good experience mounting it in the manifold... especially on 8vs


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## blown020 (Jan 9, 2009)

*Re: Hot start issue. Very irregular idle (ValveCoverGasket)*

I am running an open element sensor. Here is a picture that is not focused on the sensor, but it shows it. It is located on the rubber boot right before the throttle body. You can see the brass portion of it, all blurry


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## mjleamy (Mar 16, 2004)

*Re: Hot start issue. Very irregular idle (blown020)*

I imagine that is above the exhaust manifold - this is probably the worst place for it. You can bake a small pie there.


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## sdezego (Apr 23, 2004)

*Re: Hot start issue. Very irregular idle (mjleamy)*

Not trying to hijack your thread, but I did some investigating yesterday and took the Laptop with me, so hopefully this info may help as it sounds like we are experiencing similar issues. I took a good drive then ran into the store (15min). Came out and hot started. I did not get the log, but I watched before and after I started. IAT was not off the chart as it was 130* or so. I started and it did the same rough idle and run for about a min or so. WB readings were all over the place and mainly spiking high.
One thing I noticed before starting was that the CLT reading was high around 220*+ (even with easy therm the stock Bosch sensor is not exact), so I don't know if this has anything to do with it. i.e. maybe it is off the scale for some logic loop??
I am not doing any IAT, Baro or CLT compensation (to my recollection). I too am running an open element IAT (stock G60 IAT in in the stock position on the stock plastic intake tube)
It definitely seems like some sort of heat soak, but...
Mine is more of a small annoyance more than anything, but it sounds like yours is the same issue, but worse.
I did some minor tweaking on the VE maps around the idle area as I had not done so, since the move to 10% ethanol and it seemed to have improved the issue in open loop on hot restart, but it is still there as mentioned above.


_Modified by sdezego at 11:29 AM 10-23-2009_


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## sdezego (Apr 23, 2004)

*Re: Hot start issue. Very irregular idle (blown020)*

I wonder if this is actually ign related. i.e. Hall, rotor or coil heat soaking.
Reason being, I had strange issue one time years back with a non-bosch Rotor. The Thick film resistor would go haywire when it got hot and caused massive ign problems. I am just wondering it the heat soak could be causing a similar, but less debilitating issue but causing ign misfires?? ...maybe I am reaching now, but I know an ign misfire will produce a lean spike on the Wideband due to the unburt fuel/oxy.


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## sdezego (Apr 23, 2004)

*Re: Hot start issue. Very irregular idle (sdezego)*

What did you find out?


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## blown020 (Jan 9, 2009)

*Re: Hot start issue. Very irregular idle (sdezego)*

Completely forgot to post an update. As some of you theorized, it seems as if it was a matter of heat soak, even with the open element sensor that I've been running since day 1. 
In addition to this, I had been in denial of high volume oil consumption in cylinder 4 only. Finally the other day I checked the plug and after 1000 miles on a new plugs, it was soaked in oil. Pretty much, I think there was so much oil getting in that cylinder that is was almost drowning out any spark when cold or idling. 
I believe it was a conbination of both things that made the spiking so much more apparent. 
Last weekend I put in an RV and moved the sensor to right after the air box and the problem mostly disappeared.


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## ValveCoverGasket (Mar 20, 2002)

*Re: Hot start issue. Very irregular idle (blown020)*

good to hear its sorted http://****************.com/smile/emthup.gif


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## sdezego (Apr 23, 2004)

*Re: Hot start issue. Very irregular idle (blown020)*

Glad you found out the hot start issue at least.
I think I have found the source of mine. After looking at my Coolant Correted air density table, it was set to go leaner as CLT > 160 (up to about 90% @210*). I am not sure how I ended up with this table, but I have probably not reviewed it since I built my initial .msq (or perhaps when I switched to _hr code)... Anyway, this makes perfect sense since upon hot restarts, the CLT is high (MAT being a bit higher, but not showing heat soak as everyone and a LOT of posts in the MS forms were eluding to). This along with the fact that my bosch CLT sensor is reporting ~12* more than actual due to easy therm values (even after 5 iterations of tweaks).
So, today I gave it a go and inverted this table so that it enrichens above 170* up to 220*. Sure enough the hot restart was 99% better and today was a good test day because it is hot as heck outside. I stopped, went into the store for 10 min and then started and immediately launched the CLT config in TunerStudio and tweaked the compensation even a bit higher at 190-210 and it A/F's dropped and idle was perfect. So, I am now @ 
112% at 215, 
107% at 204
104% at 193
100% at 167 and below
Now I just need to figure out if this type of compensation is ok or if it is a bandaid.
S


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## oilpangasket (Dec 5, 2007)

*Re: Hot start issue. Very irregular idle (sdezego)*

I see you got it sorted out, but just my 2 cents.
I set my ASE after start enrichment to seconds, and have it on for a total of about 60-120 seconds. This helps keep the ASE active longer. On a couple non-boosted cars I have also found using a fixed resistor for the IAT sensor helps alot. This keeps the AFRs steady and the sensor can no longer heat soak. Open element IAT sensors that are tucked in the fender well are also a good idea. A 2- wire bosch PWM idle valve will also make life a lot easier for hot starts.


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## blown020 (Jan 9, 2009)

*Re: Hot start issue. Very irregular idle (oilpangasket)*

opg, 
Those are all things I've considered, but due to lack of time because of school I'm dealing with things how they are for the time being. Just tuning around them. I would love to wire in the ISV but school and work leave little time to play cars for now. 
The resistor though, explain more.


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## oilpangasket (Dec 5, 2007)

*Re: Hot start issue. Very irregular idle (blown020)*

On my personal car I had bad problems with even an open element IAT sensor heatsoaking even when it was in the airfilter or the fender well. I have my car setup for the stock OEM Bosch sensors, so I used a terminal block with the little screw terminals for holding wires and inserted a 2.2K ohm resistor in it. The terminal block also has two little prongs that fit nicely into the stock IAT sensor plug. This fixed my IAT at a constant 72 degrees the way I have my easy therm values setup. Now my afrs stay constant throughout the year, even in the coldest winter days. If I leave my car sit while in the store and come back out, it starts right up with no leaning out. Use a multimeter and find your IAT sensors resistance value at normal operating temp or just ambient temp and use a resistor that matches this value. I don't condone this fix, but it does help alot on some installs.
I also have an idle valve so that probably helps a lot too. 


_Modified by oilpangasket at 5:51 PM 11-19-2009_


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## sdezego (Apr 23, 2004)

*Re: Hot start issue. Very irregular idle (sdezego)*

update on mine: The CLT compensation did not correct the hot starts... I really think this is something in the extra code...


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## oilpangasket (Dec 5, 2007)

*Re: Hot start issue. Very irregular idle (sdezego)*

Your probably just going to have to either use an open element IAT sensor and mount it in the fender well, or use a fixed resistor for a fixed IAT. A PWM idle valve really helps here too. Where is your IAT sensor currently located? The intake manifold isn't really a good place especially with a closed element sensor they just heat soak.


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## sdezego (Apr 23, 2004)

*Re: Hot start issue. Very irregular idle (oilpangasket)*

Using the stock G60 open element IAT in the stock plastic boost tube at the stock location.
The logs did not show the IAT off the chart when hot starting. This last bout was with the outside temp around 60* or less outside. Same situation, go into store, come back 10-15 minutes later and hot restart idle is piss poor. A/F's are really high. After about 30 sec to a min, it clears up.
It does not appear to be IAT related.


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## sdezego (Apr 23, 2004)

*Re: Hot start issue. Very irregular idle (sdezego)*

Also, using a fixed resistor across the IAT is a very bad idea on a boosted motor and not a good idea on a non-boosted motor.


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## mjleamy (Mar 16, 2004)

*Re: Hot start issue. Very irregular idle (sdezego)*

This is an interesting thread ... what were the IAT values you saw at hot start? The fueling equation is relatively simple, so we can back out how much difference in degF to get a unit change in AFR. 
Equations necessary are below, and reproduced from the MegaManual:
REQ_FUEL*10 = 36,000,000 * CID * AIRDEN(100kPA, 70ºF)/(NCYL*AFR*INJFLOW ) * 1/DIVIDE_PULSE 
Where: 

36,000,000 is the number of tenths of a millisecond in an hour, used to get the pounds per 1/10 milllisecond from the pounds/hours rating of the injectors.
REQ_FUEL = Computed injector open time in tenths of millisecond.
CID = Cubic Inch Displacement.
AIRDEN = Air density (pounds per cubic inch) at MAP pressure of 100 Kpa, Air Temperature of 70
Degrees F, and Barometric Pressure of 30.00 In HG
NCYL = Number of Cylinders
INJFLOW = Injector Flow Rate in pounds per hour.
DIVIDE_PULSE = injection divide number for number of injections per engine cycle.
The AIRDEN function (used above) is defined by: 

AIRDEN(MAP, temp) = 0.0391568* (MAP*10-31.0)/((temp+459.7) * 1728)


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## oilpangasket (Dec 5, 2007)

*Re: Hot start issue. Very irregular idle (mjleamy)*

It isn't a good idea but I was running a pretty decent sized intercooler and rich in boost so I didn't worry.
Megasquirt seems to need a lot of fuel on warm starts so I had my ASE set for around 120 seconds and turned up the bins until it started and idled ok on warm starts. That's another reason I recommend a PWM idle valve with installs because they really help combat this type of problem. Try messing with your ASE and see if you can get it to help any. I had my ABA holding a steady 950 rpm idle with the ASE and idle valve on warm starts, but it took a lot of tweaking.
If you have ever poured fuel onto a hot engine on accident and heard it hiss and sizzle and instantly evaporate you will start to get the idea of why you need a little more fuel on a warm start up.
This is what I had mine set to, but every engine setup will require a different ASE. It takes a lot of tweaking with a combination of things to get it to start and idle on a warm start. You may have noticed that adjusting the idle on the throttlebody makes it idle ok on a warm start, but idles faster after it is driven for a while.










_Modified by oilpangasket at 2:44 PM 12-5-2009_


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## sdezego (Apr 23, 2004)

*Re: Hot start issue. Very irregular idle (mjleamy)*

I should clarify again to JIC: it is not the Hot start crank, but the hot start idle/run immediately following. Crank/start are tip top regardless.
So, on the recent log that I have (hot after start run was not as bad as it is at times), but was def lean and rough for the first 60 sec), the IAT was 127* before cranking. This was a hot day 93*. After start, the IAT really changed very little until driving. Coolant temp read 215* (see below regarding this)
I don't have a log from the other night, but as mentioned it was very cool outside - 60*. The hot after start run was terrible.
Here are my thoughts:
- the megamanual states ASE is ignored when CLT is > 170*. Even after tweaking my curve for the bosch sensor, the CLT still seems to read about +10* 
- Warm up Enrichment table stops at 160*. I am not sure if WUE is not used when hot starting and the CLT is > 160*, but I think it is ignored. I guess I could tell from the LED or Logs the next time. *EDIT:* I looked at the log from above and it states the bit Warm:N
So, I think the problem here is that there is no ASE when the CLT >160* (correct me if I am wrong). This is a problem for me.
I guess I could tweak the CLT Corrected Air density some more, but I really don;t like having to tweak this table since it affect the MAP all of the time.
I really just need the WUE or ASE to cycle in an after start regardless of CLT.
Shawn


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## blown020 (Jan 9, 2009)

*Re: Hot start issue. Very irregular idle (sdezego)*

Found the true cause of the problem. Came down to simple tuning. There was a portion of my map (low load, low rpm) that I didn't pay much attention to and hadn't tuned much, so the ecu was just searching for a stable spot therefore it was jumping around and causing the wacky idle.


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