SE Charge Cooler IAC valve
Discussion
I have for some time been having trouble with the engine management on my SE (Which is why I fancy a good old fashioned carb model). Does anyone know a sure fire way of testing the 'Idle Air Control Vave' On an SE. I have tied testing it with a digital volt meter which shows the correct resistance accross the terminals but when a current is supplied to the terminals the plunger wiggles but does not move and it is stiff in the extreme to move almost unmovable. Any thoughts?
One sure fire way to check your entire engine management system is to get yourself setup with Andy Whittaker’s “FreeScan” engine diagnostics. He offers a free download of the software on his web site. You install this software on a portable computer (with Windows 98 or later), and get the cable that is necessary to connect your computer to the ALDL lead on your car. The FreeScan software allows you to monitor and printout out a continuous log of 30 + vital engine parameters. Andy suggests that you look for things in the data that just don’t make sense. For example, you might see that there is erratic movement in the IAC position, and that the ECU is not able to achieve the desired idle RPM. This might indicate a bad IAC.
There are lots of possibilities, and if you don’t have the FreeScan setup, I would suggest that you start with the simple stuff, and those things that have the greatest possible affect on engine performance. Reset the ECU by removing (for 30 seconds) the 10 amp fuse to the ECU that is located in the rear boot. Make sure that the ignition has been turned off for 20-30 seconds prior to doing this, and after doing so take the car for a 5-10 minute mild run. The ECU can get confused about the real IAC position, and this reset process gives the ECU a chance to relearn it’s proper position. Then check the Throttle Jack/Exhaust Back Pressure Valve circuit and make sure that it is vacuum tight and functioning properly. Then, while you have the vac pump out, run a vacuum check on the MAP sensor circuit. Then disconnect the O2 sensor to see if this affects engine operation. The O2 sensor is especially suspect if you have a lot of miles on it. Then check the fuel filter for obstruction. Then check the direct ignition module and coils. Disconnect plug wires one at a time to see of you get a drop in engine RPM. Check the coils for corrosion or leaks. A lot of auto part stores will run a bench check of the ignition module for you at no charge (at least here in the US they will). Then as a last resort, check the fuel pressure, or have someone check it for you. All this can be done at little or no cost. A hand vac pump/gauge might cost $15 USD (you should probably have one of these anyway)… a fuel pressure gauge might cost $40 USD.
I hope some of this helps. Good luck...Walt '91 SE
There are lots of possibilities, and if you don’t have the FreeScan setup, I would suggest that you start with the simple stuff, and those things that have the greatest possible affect on engine performance. Reset the ECU by removing (for 30 seconds) the 10 amp fuse to the ECU that is located in the rear boot. Make sure that the ignition has been turned off for 20-30 seconds prior to doing this, and after doing so take the car for a 5-10 minute mild run. The ECU can get confused about the real IAC position, and this reset process gives the ECU a chance to relearn it’s proper position. Then check the Throttle Jack/Exhaust Back Pressure Valve circuit and make sure that it is vacuum tight and functioning properly. Then, while you have the vac pump out, run a vacuum check on the MAP sensor circuit. Then disconnect the O2 sensor to see if this affects engine operation. The O2 sensor is especially suspect if you have a lot of miles on it. Then check the fuel filter for obstruction. Then check the direct ignition module and coils. Disconnect plug wires one at a time to see of you get a drop in engine RPM. Check the coils for corrosion or leaks. A lot of auto part stores will run a bench check of the ignition module for you at no charge (at least here in the US they will). Then as a last resort, check the fuel pressure, or have someone check it for you. All this can be done at little or no cost. A hand vac pump/gauge might cost $15 USD (you should probably have one of these anyway)… a fuel pressure gauge might cost $40 USD.
I hope some of this helps. Good luck...Walt '91 SE
Thanks for your response.
The car has covered 46,000 miles I have recently fitted a new 0xygen sensor and temp sensor. Having removed the IAC valve and pushed its plunger in to its smallest length and re fitted it & re set the ECM the car now idles. The problem being the car idles high and splutters and coughs when asked to accelerate resonably quickly. I have no EBP valve as I have removed the Cat fitted a sports exhaust and blanked the vac supply pipe.
When the car would not idle when hot the car had the full performance expected of an SE. Now the car idles when hot the car has lost its brut strength.
I am hoping that the local Lotus dealer is going to put it on his Tech 1 free, he has stated he does not want to work on the car as he hates the engine managment system used on the injected Esprits and rekons when they go wrong they are a night mare to sort out but he will supply a print out from the tech 1. He is also going to check the fuel presure as the fuel pump does seem to whine quite loudly behind you when the engine is running.
Any further thoughts?
The car has covered 46,000 miles I have recently fitted a new 0xygen sensor and temp sensor. Having removed the IAC valve and pushed its plunger in to its smallest length and re fitted it & re set the ECM the car now idles. The problem being the car idles high and splutters and coughs when asked to accelerate resonably quickly. I have no EBP valve as I have removed the Cat fitted a sports exhaust and blanked the vac supply pipe.
When the car would not idle when hot the car had the full performance expected of an SE. Now the car idles when hot the car has lost its brut strength.
I am hoping that the local Lotus dealer is going to put it on his Tech 1 free, he has stated he does not want to work on the car as he hates the engine managment system used on the injected Esprits and rekons when they go wrong they are a night mare to sort out but he will supply a print out from the tech 1. He is also going to check the fuel presure as the fuel pump does seem to whine quite loudly behind you when the engine is running.
Any further thoughts?
I went through a similar thing with my ’91 SE. I had just bought it last June. It was a garage queen, and there were several things wrong with it when I bought it. But one of the things that I fixed along the way took this car from just fair performance to truly outstanding performance. That was the fuel system.
In the process of trouble shooting the car’s sluggish performance I found out that the car had bad gas in it when I had bought it. I removed the fuel filter, and found it almost completely clogged with black crud. So, I replaced the filter, and completely drained the fuel tanks. I also removed all the injectors and had them bench tested, metered and cleaned. This repair got the car to a point where it would boost to about 0.5 bar, but no more. Now, at the time I knew that this car should be able to do at least 1.0 bar of boost, because I have the S4S MK5 chip. So I was on the right trail, but there was still something wrong. By this time I had already eliminated air leaks, computer problems and ignition problems. So, it seemed that there was only one possibility left…a lack of fuel. So I ran a fuel pressure test, and sure enough, the fuel pressure was inadequate. It should have been around 60 psi, but it could only muster 35 psi. My guess is that the pump had been overworked when the fuel filter was clogged. It could only provide enough fuel for a partial boost. The computer was doing its job. It was picking up on the lean condition and was shutting things down at partial boost.
I replaced the fuel pump, and now she back to where she should be...0-60 mph in about 4.7 seconds.
I smell a rat. If any of the above sounds familiar to you, you might do well to have your fuel system thoroughly checked.
Good luck...Walt '91 SE
In the process of trouble shooting the car’s sluggish performance I found out that the car had bad gas in it when I had bought it. I removed the fuel filter, and found it almost completely clogged with black crud. So, I replaced the filter, and completely drained the fuel tanks. I also removed all the injectors and had them bench tested, metered and cleaned. This repair got the car to a point where it would boost to about 0.5 bar, but no more. Now, at the time I knew that this car should be able to do at least 1.0 bar of boost, because I have the S4S MK5 chip. So I was on the right trail, but there was still something wrong. By this time I had already eliminated air leaks, computer problems and ignition problems. So, it seemed that there was only one possibility left…a lack of fuel. So I ran a fuel pressure test, and sure enough, the fuel pressure was inadequate. It should have been around 60 psi, but it could only muster 35 psi. My guess is that the pump had been overworked when the fuel filter was clogged. It could only provide enough fuel for a partial boost. The computer was doing its job. It was picking up on the lean condition and was shutting things down at partial boost.
I replaced the fuel pump, and now she back to where she should be...0-60 mph in about 4.7 seconds.
I smell a rat. If any of the above sounds familiar to you, you might do well to have your fuel system thoroughly checked.
Good luck...Walt '91 SE
Thanks again for your response. Where is the fuel filter situated? I think I am getting full boost, But I suspect that the IAC valve is not functioning to its full extent and allowing air past it when it should be shut thus making the fuel mixture too weak. does this sound reasonable.
fuel filter is next to the bulkhead in the righ corner of the engine bay, kind of under the window- a metal canister in a line of black fuel line.
as for the IAC Walt is right- as you have removed/replaced it (and checked correct voltage) the IAC may not be lined up properly- this is a fairly common problem- the ECU is unable to sense the proper "resting spot" for the valve. This means that the plunger is in the wrong relative position (kind of like an old turn table where the arm wouldn't return to the right place if you set the wrong record rpm).
I don't have acces to my manual right now, but on previous Delco incjected cars, I have connected the IAC valve to be at "rest" by reading the voltage before connecting it again. You need to know what voltage the IAC is supposed to read to be at rest (ths is usually not zero volts!)- and yes a freescan or similar program makes this possible.
>> Edited by sydneyse on Wednesday 18th December 11:07
>> Edited by sydneyse on Wednesday 18th December 11:09
as for the IAC Walt is right- as you have removed/replaced it (and checked correct voltage) the IAC may not be lined up properly- this is a fairly common problem- the ECU is unable to sense the proper "resting spot" for the valve. This means that the plunger is in the wrong relative position (kind of like an old turn table where the arm wouldn't return to the right place if you set the wrong record rpm).
I don't have acces to my manual right now, but on previous Delco incjected cars, I have connected the IAC valve to be at "rest" by reading the voltage before connecting it again. You need to know what voltage the IAC is supposed to read to be at rest (ths is usually not zero volts!)- and yes a freescan or similar program makes this possible.
>> Edited by sydneyse on Wednesday 18th December 11:07
>> Edited by sydneyse on Wednesday 18th December 11:09
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