Rough idle when heater comes on

[Anthony]

I noticed something unusual this morning. The engine was running smooth on cold startup, but when the temp reached about 110°F and the heater started blowing, the engine began running a bit rough at the same time. It wasn't too serious, but I could feel the difference. I was still in Park when it happened. Has anyone ever experienced this or know what might be happening?

[2seater]

Get into diagnostics immediately upon a cold start to watch for the indicator it has achieved closed loop operation. I suspect that is what is happening and the heater fan engagement is coincidence. The closed loop temperature is programmed into the PROM but there is also a timer and other modifiers that kick in if there is a fault in that system. 

[2seater]

This is a thread from this previous summer about coolant temperature and closed loop. Maybe it will shed some light?

Coolant Temperature for entering closed loop - Reatta Owners Journal Forum - Reatta Owners Journal Forums

 

Edited January 22 by 2seater

[Anthony]

23 hours ago, 2seater said:

This is a thread from this previous summer about coolant temperature and closed loop. Maybe it will shed some light?

Coolant Temperature for entering closed loop - Reatta Owners Journal Forum - Reatta Owners Journal Forums

 

I haven't checked it yet because the roads are too icy and salty to take the car out, but it sounds like that is indeed what is happening. It happened at about 40C, the same as yours. 

 

Now I guess it's down to figuring out what exactly the computer is altering at that moment, and why.

[Anthony]

So here's what I found this morning:

 

Closed loop came on at 33°C and heater came on shortly after. Rough running came at same time as closed loop, so heater had nothing to do with it.

 

After closed loop came on, INT (fuel integrator) was varying from 129-136 and BLM (block learn) constant at 121. I wasn't aware that one could be above 128 and the other below 🤔. Doesn't make a lot of sense to me 🤷.

 

Injector pulse width seemed unstable, oscillating by 0.3 up and down over and over again, while gradually moving from 4.3 at the lowest to 5.1 at the highest, then suddenly back down to around 4.6.

 

Something interesting I noted was that OLDPA3 (knock count) was at 9999. 

[Ronnie]

The main thing that happens when the engine goes into closed loop is the ECM starts looking at the signal it gets from the O2 sensor. All the odd readings you are getting may be because of a O2 sensor failing. If you have any doubts about the O2 sensor being good I would replace it and see if that cures the problem.

[rogold]

Could it be a vacuum leak in the HVAC programmer behind the glove box?

 

[Anthony]

2 hours ago, Ronnie said:

If you have any doubts about the O2 sensor being good I would replace it and see if that cures the problem.

 

2 hours ago, rogold said:

Could it be a vacuum leak in the HVAC programmer behind the glove box?

 

I will check both of these. Thank you

[2seater]

3 hours ago, Anthony said:

So here's what I found this morning:

 

Closed loop came on at 33°C and heater came on shortly after. Rough running came at same time as closed loop, so heater had nothing to do with it.

 

After closed loop came on, INT (fuel integrator) was varying from 129-136 and BLM (block learn) constant at 121. I wasn't aware that one could be above 128 and the other below 🤔. Doesn't make a lot of sense to me 🤷.

The integrator and block learn are not fixed numbers, with the integrator being the most dynamic. The integrator is the instant adjustment so it dancing around in the area of 128 (the target) is normal. The block learn is the long term adjustment. In this case, in the example above, the integrator is very slightly rich, (number greater than 128), so the block learn is adjusting to a more lean (below 128) reading to compensate. Rarely is the idle value as close as yours appears to be and I think the operation is normal. If you increase engine speed, the numbers should change because there are multiple cells in the ECM that keep track of the long term operating conditions. The cross counts of the O2 sensor shows you how many times the reading goes rich and lean, which is normal, and the more often, the better. 

3 hours ago, Anthony said:

 

Injector pulse width seemed unstable, oscillating by 0.3 up and down over and over again, while gradually moving from 4.3 at the lowest to 5.1 at the highest, then suddenly back down to around 4.6.

Pulse width is usually more stable at a base idle but some variance is normal as the ECM adjusts the fueling. I would believe it is a reaction to the rough running you are feeling, not the cause.

3 hours ago, Anthony said:

Something interesting I noted was that OLDPA3 (knock count) was at 9999. 

The knock count isn't normal. It should reset to zero upon turning ignition on and it is normal for it to register up to a few hundred counts from the internal noise from starting, but then it should not be advancing further while running under little to no load. Try looking at the number with just the ignition on but do not start the engine. Is there any spark retard indicated in ED16 while running?

 

The advice about the O2 and vacuum leaks is on target.

[Anthony]

56 minutes ago, 2seater said:

The knock count isn't normal. It should reset to zero upon turning ignition on and it is normal for it to register up to a few hundred counts from the internal noise from starting, but then it should not be advancing further while running under little to no load. Try looking at the number with just the ignition on but do not start the engine. Is there any spark retard indicated in ED16 while 

When I checked that data point a few weeks ago, OLDPA3 was at 0 before startup, jumped 600-700 while starting, then another similar large jump when I tapped on the engine with a wrench. Manual says it should go to 255, then repeat, but doesn't say what to do if it goes above 255.

 

This latest time it somehow reached 9999 just sitting there in park after startup, without tapping on the engine at all. 

 

Spark retard showed 0° in both cases. 

[2seater]

9 hours ago, Anthony said:

When I checked that data point a few weeks ago, OLDPA3 was at 0 before startup, jumped 600-700 while starting, then another similar large jump when I tapped on the engine with a wrench. Manual says it should go to 255, then repeat, but doesn't say what to do if it goes above 255.

 

This latest time it somehow reached 9999 just sitting there in park after startup, without tapping on the engine at all. 

 

Spark retard showed 0° in both cases. 

Hmm, that is a bit odd. I have never seen a figure quoted for the number of knock counts to be expected when starting?? The range listed in system diagnosis chart isn't a guide for what to expect but it is written to imply it is? Some knock is registered when starting and you tested the sensor so we know ii is working. Was the Knock sensor recently replaced or removed and reinstalled? If overtightened, it can become hypersensitive. Is the ignition timing steady at idle? It may change (reduce) some as the engine warms up but should be stable at around 20 degrees, or a bit more, and increase a couple of degrees when put in drive to pick up the engine load.

[Ronnie]

13 hours ago, Anthony said:

This latest time it somehow reached 9999 just sitting there in park after startup, without tapping on the engine at all.

Disconnect the sensor and do the test again. I suspect you might get the same results.

[Anthony]

I've been monitoring the data as I run errands today. Here's what I found so far:

 

I haven't been able to duplicate the OLDPA3 9999 issue. I suppose it is intermittent. I did find out that it goes up by several hundred each time the engine is cranked, then seems to stay at that figure for the rest of the trip. It would be interesting to know what the knock counts are supposed to be. 

 

On the previously mentioned trip when I noticed it at 9999, I had only cranked it once though.  I will try wiggling the wires or unplugging it, as Ronnie suggested, to see what happens. I didn't get any service records with the car, so I don't know if it's ever been replaced. 

 

I found out there are actually two different spark readings. One is about 20 at idle and goes up to the 40s as rpm increases. The other, called Spark Angle is what I was looking at before, and it stays at 0 all the time. From what I read, that one only increases if knock is detected.

 

The O² sensor is giving very weak, erratic readings. The cross counts don't match up to graphs that I've seen online. It frequently has 0 cross counts, mostly at idle, but even while going down the road, it will fall from a high number, like 17, down to zero for a second or two. The graphs I've seen online oscillate at a steady rate, when all other variables are held constant. I will take it out and inspect it.

 

I'm still trying to wrap my head around how it works. I haven't heard a good explanation of why the voltage is supposed to go up and down. I have noticed that it seems to be related to RPM, so I wonder if the cross counts should match the exhaust strokes. If that's the case, then I would presume that 0 should never be seen at driving speeds, except in case of an extreme and constant lean or rich condition.

 

I feel a slight miss, if that's the right term (slight vibration of the steering wheel every second or so at idle), even before it goes into closed loop, so that makes me think maybe the fuel injectors should also be cleaned and checked to see if one is clogged or leaking. 

 

HVAC vacuum check is still on the to-do list.

 

I also bought a new positive battery terminal to replace the rusted one when time permits. 

Edited January 27 by Anthony

[2seater]

1 hour ago, Anthony said:

I've been monitoring the data as I run errands today. Here's what I found so far:

 

I haven't been able to duplicate the OLDPA3 9999 issue. I suppose it is intermittent. I did find out that it goes up by several hundred each time the engine is cranked, then seems to stay at that figure for the rest of the trip. It would be interesting to know what the knock counts are supposed to be

There is no recommended minimum or maximum number, but it is normal to register a couple hundred counts from the noise created while starting. I would think that more or less cranking time would change the averages any particular engine will see. That 0-255 number in the diagnostics is a function of the range of the counter in binary terms. It is not a range in and of itself. I am not computer savvy enough to explain better than that. The figures you are seeing are normal.

1 hour ago, Anthony said:

 

On the previously mentioned trip when I noticed it at 9999, I had only cranked it once though.  I will try wiggling the wires or unplugging it, as Ronnie suggested, to see what happens. I didn't get any service records with the car, so I don't know if it's ever been replaced. 

 

I found out there are actually two different spark readings. One is about 20 at idle and goes up to the 40s as rpm increases. The other, called Spark Angle is what I was looking at before, and it stays at 0 all the time. From what I read, that one only increases if knock is detected.

The running spark advance is contained in a grid containing hundreds of individual cells. Each cell is an individual unit not related to the others around it. The grid, or table, has rpm for the vertical axis and a figure called LV8 for the horizontal axis. LV8 is a figure created by the programming using multiple inputs that estimate engine load. It is absolutely normal operation as you described above.

 

Spark angle is actually spark retard and is the amount subtracted from the normal spark advance when knock is encountered. Some knock is fleeting and expected and even though some knock counts might show up, it isn't enough to trigger a reduction in timing. 

1 hour ago, Anthony said:

 

The O² sensor is giving very weak, erratic readings. The cross counts don't match up to graphs that I've seen online. It frequently has 0 cross counts, mostly at idle, but even while going down the road, it will fall from a high number, like 17, down to zero for a second or two. The graphs I've seen online oscillate at a steady rate, when all other variables are held constant. I will take it out and inspect it.

 

I'm still trying to wrap my head around how it works. I haven't heard a good explanation of why the voltage is supposed to go up and down. I have noticed that it seems to be related to RPM, so I wonder if the cross counts should match the exhaust strokes. If that's the case, then I would presume that 0 should never be seen at driving speeds, except in case of an extreme and constant lean or rich condition.

I don't know what graphs that are presented online, but be certain they represent readings for a 35-year-old engine management system. Our ECM is light years from modern systems in computing speed and capacity. For example, modern systems use heated O2 sensors to maintain sensor operation when the engine is cool and/or the exhaust cools off like from prolonged idling. Our simple inexpensive one wire O2 sensor generates a small voltage that adds or subtracts from the reference voltage the ECM creates and it must have exhaust heat to make it operate. With increased rpm comes greater exhaust heat. The center point is somewhere in the .40v-.50v range and represents a lambda of 1.0, or stoichiometric. If the ED07 voltage indicates above the center point it is rich, if below, it is lean. It constantly swings between rich and lean, with the crossover seen in cross counts. The ECM does learn and that is why the integrator and block learn figures change over time. Even changing from 10% ethanol, to 15% or zero percent will require the system to make adjustments. Al gasoline is not created equal.

1 hour ago, Anthony said:

 

I feel a slight miss, if that's the right term (slight vibration of the steering wheel every second or so at idle), even before it goes into closed loop, so that makes me think maybe the fuel injectors should also be cleaned and checked to see if one is clogged or leaking. 

 

HVAC vacuum check is still on the to-do list.

 

I also bought a new positive battery terminal to replace the rusted one when time permits. 

If the battery is disconnected, all of the adjustments built up over time in the ECM, are reset back to a starting point that is hard wired into the system. It is safe for the engine to operate but it is not running at it's optimum until the ECM has relearned the proper adjustments and it takes a little time for that to happen while driving, not just idling.

[Anthony]

13 minutes ago, 2seater said:

Even changing from 10% ethanol, to 15% or zero percent will require the system to make adjustments. Al gasoline is not created equal.

I sucked all the gas out of the tank through my fuel pressure gauge, to eliminate the possibility of old gas or water contamination, and replaced it with non-ethanol. They say it can be stored longer than the ethanol blends before it goes bad, which is good since I don't drive too much. 

[Anthony]

I found this while sorting out all the technical service bulletins for the car (a 5" thick stack of printouts 😵). 

 

 

[2seater]

Interesting information, thanks.

I just replace the sensor as a matter of maintenance. All the work is in the removing and replacing it and I do not have the test gear as described above. I guess I do have a handheld o'scope that would generate a similar wave form but not the hookup that the technicians would use. For a sensor that is less than $20,  testing would make sense if it fails to do better, but from the limited information so far, the original is working.

[DAVES89]

I'm not as smart as you guys. I start with what's simple and easy first and work my way to the hard things. 

 So to start I tighten the battery connections, check and clean the grounds, remove the Delco coil pack and ignition module and clean the grounding plate and idle air control and chamber.

 If that doesn't do it then I start with swapping the MAF Sensor, then drive the car a bit. If that's not it then I swap out the coil pack and ignition module then drive it a bit. Then I swap out the O2 sensor and drive it some more. Last is plugs and wires because I keep a log in each Reattas owners manual on service interval.

 But the big difference is that all the parts that are swapped in are previously tested by me before I have a problem. I go to a salvage yard get the part install it and take the working part and put it in storage. Exception is the O2 sensor, those I buy new.