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90 Reatta idle surging after going into closed loop


drdelsol

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I have a 90 that we got a few months ago. 140k. It was running great, nicer car then our 91, but it started surging and would die at low rpms. We bought it from a mechanic who had replaced a lot of parts but then he needed hurricane Ian money. No, it didn't get flooded. It starts and runs smooth during fast idle but when it warms up a couple minute , I am guessing this is when it goes into closed loop, and the idle drops it surges and will die if you dont up the rpms to over 1500. The coils are fairly new as is the ICM, getting spark from each. Plugs and wires recently replaced. Cleaned the AIC and EGR according to the guides. Vacuum hoses appear replaced and sprayed around them with no change, as well as around intake gasket area.  Got a TPS code once, replaced and adjusted that and did the oxygen sensor at the same time. No codes but no improvement. Fuel pressure checked and good. Fuel filter looks shiny and recent a box for one was in the trunk. Unplugged the MAF and it would keep running, albeit a little rough. Put on a new delphi MAF yesterday, no change. Read about unplugging the 02 sensor to prevent closed loop but that did nothing either but that was with the engine warm too I think. Can hear the egr clicking through diagnostics and the IAC clicks, though a lot faster then the EGR.  I have not considered the crank or cam sensor due to how well it runs at fast idle in open loop. This isn't the exact order I did everything, just trying to remember everything I've checked.

 

Any suggestions? Another sensor that comes on in closed loop I am forgetting?  Thanks in advance.

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Welcome to the forum!!

 

Start the engine and go into diagnostic mode. Keep the engine running with the throttle to prevent it from dying if you have to. Once in diagnostics and code checks have completed, go to ECM overrides. Select ES09 to control the IAC motor. Adjust the engine RPM to about 750 and see if the engine will maintain that RPM or if the fluctuation starts while you are overriding the IAC. Let us know what results you get.

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ok,I feel stupid. I think I might have just got upset the new MAF didnt make it like new yesterday and I didn't check codes again. Today I went out and first thing did the IAC override and could adjust the idle a bit playing with it, no surging. But, I keep getting the MAF code now with the new one. It is idling at about 750 with no surging but it is not as smooth and sometimes it bogs a little getting up to 1500. It is afternoon thunderstorms here so only played with it sitting in park a/c off. Could the new MAF be better but not fantastic?

Thanks again so much for the help

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Something is not right if you are getting a MAF code that is current. Make certain you have the correct MAF sensor. Then check for a good connection at the MAF. Clear the codes again and see if it comes back.

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Agree with all of the above. If the MAF is giving trouble, disconnecting it should stabilize things. It may not run well, but it should at least be consistent. You can read the MAF at a constant rpm in park also. If the idle is rolling, the MAF will do so as well making it a little tough to separate cause from effect. Usually warm idle is in the mid single digits, like in the 4-6 range. Too bad you can't swap MAF's with the 91 but the styles are different, although the sensor covers the exact same range and frequency. Is the Delphi MAF actually new or a remanufactured unit?

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It is supposed to be new. I will double check the part number. It is running about like it did when I disconnected the old one but slightly lower RPM. The old one wasn't throwing a code but had the surging then. No surging now. I will check the wiring and diagnostics again. 

Thanks again for the help. My wife really likes these cars and was using it as her daily driver.

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30 minutes ago, drdelsol said:

It is supposed to be new.

That sounds like you may have some doubts about if it new. If it was bought new at an auto parts store and the code persists, I would return it as defective and try another one. Delphi is the brand I prefer.

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I was curious to see what was available from Rock Auto for example. It looks like there are all sorts of players, with primarily Cardone listing remanufactured. ASSume the others are new? Pretty certain the OE for the sensor is Hitachi , which I know isn't helpful, but I noticed some illustrations are not for the correct sensor style. I don't know what that all means but it's hard to believe there are that many places making new sensors for over thirty year old engine configurations? The sensor style changed with the Series 1 engine, also Hitachi. I have a handful from the salvage yard.

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The MAF is the Delphi off Rock Auto. It had a sticker no returns after you open it. Today it died with the new MAF plugged in, running a bit rough and around 800 rpms with it unplugged but no stalling. Got the code 34 with it plugged in. No visible wire problems near the connector and sprayed contact cleaner on it. Got 5 volts terminal a, 12 between b and c and 12 individually b and c to battery. So, this sensor sucks? Noticed this one made in China.

Edited by drdelsol
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Ok. With that new MAF sensor plugged in now it's no longer throwing a code, at least not these last few cycles. Idling a little rough but put it in gear and the surging and dying is back. No codes

Edited by drdelsol
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When running with the sensor plugged in, tap on it moderately hard to see if it has an effect on the idle. That's what we used to do many years ago. Have you watched the MAF reading at warm idle? Usually in the middle single digits, like 4-6gr/sec and relatively steady. I know you mentioned a new TPS. What is the idle voltage? I saw mention of the EGR clicking too. The EGR should not be active at idle, no clicking to be heard.

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Not sure how much it matters, but I remember reading in the factory repair manual once that the MAF sensor and the metal piece it attaches to are a matched set and cannot be replaced independently. Could that possibly be what's going on? 

 

I'll see if I can find it again.

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11 hours ago, Philbo said:

Not sure how much it matters, but I remember reading in the factory repair manual once that the MAF sensor and the metal piece it attaches to are a matched set and cannot be replaced independently. Could that possibly be what's going on? 

 

I'll see if I can find it again.. 

You are correct, the FSM does say that. I have swapped several sensors, used different style sensors, including inline 3" diameter ones, but as long as the signal frequency is in the expected and correct range, the ECM doesn't care. It is possible there may be slight calibration variation, but the overall system is redundant and accommodates this without issue. 

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The egr was tapping when I was in override checking it. Tapping maf didn't make a difference.  Maf reading was 5.8 I think at Wark idle. Just put a new IAC in, sitting in the car now. At first it was terrible. Disconnected the battery.  Now the idle is good no surging or dying. It revs smoothly. Try to drive it around the block it surges again and died pulling back into driveway. No codes at all. Now it is idling nice in gear with the ac on in my driveway at 600 rpms. Could it just need to computer to learn a bit more driving?

Edited by drdelsol
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18 minutes ago, drdelsol said:

Could it just need to computer to learn a bit more driving?

It does have to go through a learning process so maybe that is all it needs.

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Ok. Drove around the neighborhood for a while, dying at every stop sign. It starts right back up with just a touch of the key. Back home sitting in gear it seems to hate rpms starting at about 1500 then it tries to die. In park or neutral no hesitation,  smooth up to 3000. Stopped In gear a few seconds at 1500 it will just surge a bit and die. Time to try a new ECM?

Edited by drdelsol
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Today I swapped to coils and ignition module from the 91. Made no difference,  maybe a little worse but the unit on it is practically new. Cycling fuel injectors gave noticeable degradation in idle as each switched off. So with new IAC, O2 sensor, throttle position sensor and MAF I can enjoy it sitting in idle with the air on. Put it in gear get to 1300 or so RPMs and it stubles and dies even if you put it back in neutral or park. Start it again and it idles nice again and will go smoothly past 2000 rpms. No codes at all. If I need a new ECM, any tips. I see some say local programming required, or might be required.

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I am going to assume the fuel pressure was checked with a gauge and the new TPS is in the .38-.42v range at idle. It is hard to say if the ECM is acting up, but one thing can be done short of doing so and that is remove the ECM, remove and reinstall the Prom and clean the connections to the ECM and reinstall wiring connections. Be sure to disconnect battery ground before working with ECM. The ECM can be left hanging from the harness to see if that helps the running. It also keeps the ECM cooler while testing. No programming is required for a replacement ECM but the existing prom will need to be switched to the new ECM. I had some Prom communication issues last year but I was actively burning chips and fiddling with tuning and I got some very strange behavior, vaguely similar to yours, but...?

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Thanks. I'll try that before I spend more money. the TPS is adjusted correctly. I did the lend a tool and fuel pressure was good. I was just out there in it for an hour with the a/c on sewing on a new steering wheel cover idling fine. then put in in gear, no change, rev it to 1300 and it died.

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