Hello, again. I have another question about the 740 1990 volvo. I am getting pretty low rpms for this car. The rpms will only go up to 1500. I already check the fuel pump, the fuel filter and the mass air flow sensor. Do any of you guys have any idea of why the rpms are so low? I would really appreciate any ideas you can give me.
Thanks.

I had a similar problem on my Porsche 944. It was caused by a defective throttle position switch. The computer thought that the throttle was closed with the engine at 1800 rpm and "identified" this as a trailing throttle condition, like what you get when taking your foot off the gas when exiting the freeway. The computer is programmed to shut off the injectors in this situation to save gas.

Replacing the TPS solved the problem.

Check the O2 sensor and for a blocked cat converter. I am assuming it is firing on all 4 cyl. If the tail pipe is very black, probably O2.
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95 854T, 88 780, 88 245

O2 sensor is not going to cause the engine to not exceed 1500 rpm. A blocked cat certainly will though. A vacummn gauge will tell you very quickly. You can remove the plug on the cat and see if there is an improvement also.
I would also make sure throttle butterfly is opening completely when pedal is depressed.